Important Terms and Key Points
1. Element: A substance that cannot be separated into simpler substances and that singly or in combination constitute all matter.
2. Periods: It is a horizontal row of periodic table. 3. Groups: It is a vertical column of the periodic table.
4. Atomic mass: Atomic mass of an element is the sum of protons and neutrons.
5. Atomic radius: It is defined as the distance from the centre of nucleus to the outermost shell of the atom. It is generally expressed in Picometer (pm).
6. Periodicity: The recurrence of similar physical and chemical properties of elements when arranged in a particular order.
7. Valency: It is defined as the combining capacity of an atom of an element to acquire the next inert gas configuration.
8. Electronegativity: The relative tendency of an atom to attract shared pair of electrons towards itself.
9. Electron affinity: The amount of energy released when anelectron is added to an isolated gaseous atom.
10. Ionisation energy: The amount of energy required to remove
most loosely bonded electron from an isolated gaseous atom.
11. Isotopes: Atoms of same element having similar atomic number
but different atomic mass.
12. Isobars: Atoms of different elements having different atomicn umber but same atomic mass.
Multiple Choice Questions
13. The Law of Octaves was applicable upto which element in the Periodic table:
(a) Oxygen
(b) Calcium
(c) Cobalt
(d) Potassium
Ans. (b) Calcium.
Explanation : Newland’s law of octaves was applicable only to lighter elements having atomic masses up to 40 u i.e., up to calcium. After calcium, every eighth element did not possess properties similar to that of the first element.
14. According to Mendeleev’s Periodic Law, the elements were arranged in the periodic table in the order of: [NCERT, Exemplar]
(a) Increasing atomic number
(b) Decreasing atomic number
(c) Increasing atomic masses
(d) Decreasing atomic masses
Ans. (c) Increasing atomic masses.
Explanation : According to Mendeleev’s periodic law, the elements were arranged in the periodic table in the order of increasing atomic masses.
15. In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the perioidc table later.[NCERT, Exemplar]
(a) Germanium
(b) Chlorine
(c) Oxygen
(d) Silicon
Ans. (a) Germanium.
Explanation : Chlorine, oxygen and silicon were included in Mendeleev’s periodic table. Germanium was discovered later which fit into the empty spaces left by Mendeleev and matched to the expected properties.
16. How many elements were arranged by Mendeleev in his periodictable ?
(a) 98
(b) 63
(c) 42
(d) 21
Ans. (b) 63.
Explanation : Mendeleev included 63 known elements arranged it according to increasing atomic weight; Mendeleev also left spaces for as yet undiscovered elements for which he predicted according to the atomic weights.
17. What type of oxide would Eka– aluminium form ? [NCERT, Exemplar]
(a) EO3
(b) E3O2
(c) E2O3
(d) EO
Ans. (c) E2O3
Explanation : Aluminium is Al having the oxidation state: +3, it can form Al3+ and it has valency = +3. So it will form Al2O3. Gallium and aluminium belong to the identical group and hence their valency is also going to the same which is 3. Eka Aluminium comes afterAluminium, and it is called Gallium. E2O3 is the type of oxide Eka– aluminium would form.
18. Which element was not known when Mendeleev proposed his classification ?
(a) Hydrogen
(b) Sodium
(c) Calcium
(d) Germanium
Ans. (c) Germanium
Explanation : The elements which were unknown when Mendeleev gave his classification were geranium, gallium and scandium. He left gaps for the unknown elements and predicted correctly the properties of some of the unknown elements.
19. According to Mendeleev’s Periodic Law, the elements were arranged in the periodic table in order of their:
(a) increasing atomic number
(b) decreasing atomic number
(c) increasing atomic mass
(d) decreasing atomic mass
Ans. (c) increasing atomic mass
Explanation :
Mendeleev realized that the chemical and physical properties ofelements were related to their atomic mass in a 'periodic’ way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table. So, according to Mendeleev’s periodic table elements were arranged according to their atomic mass.
20. Which of the following statements about Newland‘ slaw of octaves is correct?
(a) It was applicable to all elements.
(b) It was applicable to elements up to calcium only.
(c) Every first and seventh element had similar properties.
(d) Noble gases werediscovered that time
Ans. (b) It was applicable to elements up to calcium only.
Explanation :
Out of the total 56 known elements, Newland could arrange elements only up to calcium. Every eighth element did not show properties similar to that of the first after calcium.
21. In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later?
(a) Chlorine
(b) . Silicon
(c) Oxygen
(d) Germanium
Ans. (d) Germanium
Explanation :
Chlorine, oxygen and silicon were included in Mendeleev's periodic table. Germanium was discovered later which fit into the empty spaces left by Mendeleev and matched to the expected properties.
22. The law of octaves was given by ___.
(a) Mendeleev
(b) Newlands
(c) Bohr
(d) Moseley
Ans. (b) Newlands
Explanation :
The law of octaves was given by Newlands.
23. The position of element in the periodic table is generally determined by its:
(a) no of valence electrons
(b) no of shells
(c) both (a) and (b)
(d) none of the above
Ans. (c) both (a) and (b)
Explanation :Electronic configuration is the arrangement of electrons in the shells. Outer electrons tells us about thegroup number and the number of shells tells us about period number.
24. Vertical columns in a periodic table are called:
(a) rows
(b) periods
(c) groups
(d) patters
Ans. (c) groups
Explanation :
Horizontal rows in the periodic table are called periods and vertical columns are called groups.
25. The elements having seven valence electrons in their outermost shell are known as:
(a) alkalis
(b) halogens
(c) alkaline earth metals
(d) noble gases
Ans. (b) halogens
Explanation : The family of elements having seven electrons in the valence shell is halogens, i.e., chlorine, fluorine, bromine, iodine, astatine. Halogens are the most electronegative elements in the periodictable.
26. Non metals usually forms :
(a) acidic oxides
(b) basic oxides
(c) neutral oxides
(d) amphoteric oxides
Ans. (a) acidic oxides
Explanation : Non-metals react with oxygen to form acidic compounds of oxides which are held together by covalent bonds. These compounds can also be called as acid anhydrides.
27. The number of shells in elements of the third period is:
(a) three
(b) two
(c) four
(d) one
Ans. (a) three
Explanation : Number of shells= Period number
28. Which of the following group has the maximum radii in a group when considered in the same period?
(a) Halogens
(b) Alkaline earth metals
(c) Alkali metals
(d) Noble gases
Ans. (c) Alkali metals
Explanation : Atomic radii decreases on moving across a period from left to right ,so moving from group 1 to 18 atomic radii decreases and group 1 has the largest atomic radii as compared to the other groups of the same period.
29. An element X has 4 shells and 3 valence electrons.What is its period number?
(a) 3
(b) 5
(c) 6
(d) 4
Ans. (d) 4
Explanation :
Number of shells= Period number
30. The electronic configuration of an element M is 2, 8, 4. In modern periodic table, the element M must be placed in:
(a) 4th group
(b) 2nd group
(c) 14th group
(d) 18th group
Ans. (c) 14th group
Explanation : In the periodic table, elements having 4 valence electrons are placed in group 14.
31. Which group elements are called transition metals?
(a) Group number 1 to 2
(b) Group number 13 to 18
(c) Group number 3 to 12
(d) Group number 1 to 8
Ans. (c) Group number 3 to 12
Explanation : The elements occurring in group 3 to 12 are named as transition metals because they are metallic elements that form a transition between the main group elements, which occur in groups 1 and 2 on the left side, and groups 13–18 on the right side of the periodic table.Transition elements have following properties:
(a) They are good conductors of heat and electricity.
(b) They can be hammered or bent into shape easily.
(c) They have high melting points (but mercury is liquid at room temperature).
(d) They are usually hard and tough.
(e) They have high densities.
32. Elements of which group has only 2 shells and both are completely filled?
(a) Helium
(b) Neon
(c) Calcium
(d) Boron
Ans. (b) Neon
Explanation : Neon with the atomic number 10, has the electronic configuration as 2,8. Hence, both its K and L shells are completely filled.
33. The elements A, B and C belong to group 2, 14 and 16 respectively, of the periodic table. Which two elements of these will form covalent bonds?
(a) A and B
(b) B and C
(c) C and A
(d) None of these
Ans. (b) B and C
Explanation : The covalent bond is formed by the sharing of electrons betweentwo atoms. As the element B (which belongs to group 14) has 4 valence electrons which it can share with two atoms of the elements of C (from group 16 each having 6 valence shell electrons) to complete the octet of each included atom, B and C will form covalent bond with each other.
34. An element M is in group 13th of the periodic table. The formula for its oxide is:
(a) MO
(b) M2O3
(c) M3O2
(d) None of these
Ans. (b) M2O3
Explanation : As the element M belongs to group 13th of the periodic table so it has 3 valence electrons, i.e., it can have +3 oxidation state while oxygen atom (with 2 valency) has −2 oxidation state. So the formula for the corresponding oxide is M2O3.
35. Which of these belong to the same period? Element A B C Atomic number 2,10,5 respectively.
(a) A, B
(b) B, C
(c) C, A
(d) A, B and C
Ans. (b) B, C
Explanation : B= 10 (2, 8), C = 5 (2, 3) Both have 2 shell, so they both belong to same period.
36. Carbon belongs to the second period and group 14 while silicon belongs to the third period and group 14 of the periodic table. If atomic number of carbon is 6, the atomic number of silicon should be:
(a) 7
(b) 14
(c) 24
(d) 16
Ans. (b) 14
Explanation :
Silicon and carbon belong to the same group. They have same number of valence electron in their outermost shell i.e. 4. Hence, they will differ in atomic numbers by 8. So, 6 + 8 = 14.
37. Consider the following elements 20Ca, 8O 18Ar, 16S, 4Be, 2He Which of the above elements would you expect to be in group 16 of the Periodic Table?
(a) 20Ca and 16S
(b) 20Ca and 8O
(c) 18Ar and 16S
(d) 8O and 16S
Ans. (d) 8O and 16S
Explanation :
The electronic configuration of oxygen and sulphur is 2,6 and 2,8,6 respectively. Both of them have 6 electrons in their outermost shell. To know the group number 10 is added. The output is 16.Therefore both of them belong to group 16.
38. The atom of an element has electronic configuration 2, 8, 7. To which of the following elements would it be chemically similar?
(a) N(7)
(b) P(15)
(c) Na(11)
(d) F (9)
Ans. (d) F (9)
Explanation :
Electronic configuration of chlorine and the given element is 2,7, and 2,8,7. Both are having same number of valence electron. Hence they would be similar in their chemical property.
39. How many groups are there in the periodic table?
(a) 18
(b) 8
(c) 28
(d) 17
Ans. (a) 18
Explanation :
Vertical columns of the periodic table are known as groups. There are 18 groups in the periodic table.
40. Atomic mass number is equal to the:-
(a) total number of p and n
(b) total number of p and e
(c) number of Protons
(d) number of neutrons
Ans. (a) total number of p and n
Explanation :
Mass number is the sum of the number of protons and the number of neutrons in an atom.
41. Five elements A, B,C,D and E have atomic numbers 2,3,7,10and 18 respectively. The elements which belong to the same period of the periodic table are:
(a) A,B,C
(b) B, C,D
(c) A,D, E
(d) B,D,E
Ans. (b) B, C,D
Explanation :
B,C and D ,with atomic number 3,7,10 respectively, belong to the same period of periodic table .This is because the elements B,C and D have the same valence shell (L).
42. The alkaline earth metal present in group 2 and period 3 of the periodic table is:
(a) sodium
(b) magnesium
(c) calcium
(d) potassium
Ans. (b) magnesium
Explanation :
The alkaline earth metal present in group 2 and period 3 of the periodic table is magnesium.
43. The position of three elements A, B and C in the Periodic Table are shown below:
Which type of ion, cation or anion, will be formed by element A?
(a) cation
(b) anion
(c) both (a) and (b)
(d) none of these
Ans. (b) anion
Explanation :A will form an anion as it accepts an electron to complete its octet, and achieve the nearest gas configuration.
44. Given below is the electronic configuration of two elements. Which of these will be more electronegative?
A = 2,3 B = 2,3,5
(a) A
(b) B
(c) Both (a) and (b)
(d) None of these Ans.
(a) A
Explanation : Nitrogen is more electronegative than phosphorus, because onmoving down a group, the number of shell increases and electronegativity also decreases.
45. Where would you locate the element with electronic configuration 2,7 in the Modern Periodic Table?
(a) Group 8
(b) Group 9
(c) Group 18
(d) Group 10
Ans. (b) Group 9
Explanation :
It is the electronic configuration of Fluorine with atomic number 9. It is the hologen and is most electronegative elements.
46. The atomic number of element of second period and sixth group is ?
(a) 20
(b) 56
(c) 38
(d) 55
Ans. (b) 56
Explanation :
The element of second period and sixth group is Barium.
47. Which of the following elements do not belong to same group?
(a) P, As
(b) Tc, Re
(c) Ag, Hg
(d) Ne, Xe
Ans. (c) Ag, Hg
Explanation : Ag and Hg do not belong to same group. Ag belongs to group 11 and Hg belongs to group 12 of the periodic table.
(i) How many metals are there in the group?
(a) 1
(b) 2
(c) 3
(d) 0
Ans. (c) 3
Explanation : Sn, Pb and Fl are metals
(ii) Which type of bond is formed by elements if this group?
(a) Ionic
(b) Covalent
(c) Coordinat
(d) Metallic bond
Ans. (b) Covalent Explanation
The group is having valence of 4. So, covalent bond is formed
49. In the following set of elements, which one of the following element does not belong to the set
Calcium, Magnesium, Sodium, Beryllium
(a) Calcium
(b) Magnesium
(c) Sodium
(d) Beryllium
Ans. (c) Sodium
Explanation
Sodium does not belong to the set. This is because all otheelements belong to group 2 but sodium belongs to group 1 of the periodic table
50. Which of the period in periodic table has only gaseous elements
(a) 1
(b) 2
(c) 3
(d) 4
Ans. (a) 1
Explanation
It contains two elements H and He, both are gases
51. Which amongst the given below elements does not belong to the same period
6P12, 7Q14, 8R16, 11S23
(a) P, Q and
(b) P and
(c) P ,Q, R and
(d) Q and R
Ans. (a) P, Q and R
Explanation
The electronic configuration of the elements is given as: Element Atomic Electronic number configuration
P 6 2, 4
Q 7 2 , 5
R 8 2, 6
S 11 2, 8, 1
Element P, Q and R have only two electrons shells and hence, they belong to the same period i.e, 2nd Periodic.
52. Identify the nature of the element:
Period = 3 Valency = 4
Physical property = hard
Nature of compounds : Oxide- acidic halide - covalent.
(a) Metal
(b) Non-metal
(c) Metalloid
(d) Inner Transition elements
Ans. (c) Metalloid
Explanation :
The element is silicon with atomic number 14. It belongs to 3rd period and its valency is 4. It is a metalloid and exhibit properties of both metals and non-metals. It forms covalent halides as its outermost shell has 4 electrons.
53. Where would you locate the element with electronic configuration 2, 8 in the Modern Periodic Table?[NCERT, Exemplar]
(a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10
Ans. (c) Group 18.
Explanation :
Element with the electronic configuration of 2, 8 is Neon having the atomic number 10. In the modern periodic table, noble gas elements are present in the group 18. Hence, the element with electronic configuration 2, 8 will be in the 18th group of the Modern Periodic Table.
54. The outermost shell for elements of period 2 will be:
(a) K shell
(b) L shell
(c) M shell
(d) N shell
Ans. (b) L shell.
Explanation : The elements having two valence shells are placed in the second period. Thus, the outermost shell of these elements is L-shell.
55. An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be:*
(a) Group 1 and Period 3
(b) Group 2 and Period 3
(c) Group 13 and Period 3
(d) Group 16 and Period 3
Ans. (d) Group 16 and Period 3
Explanation :
An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be placed in the group 16 and 3rd period of the periodic table since the elements of the group 16 forms the acidic oxides.
56. The number of electrons in the valence shell is equal to its …………
(a) atomic mass
(b) group number
(c) period number
(d) atomic volume
Ans. (b) group number.
Explanation :
The number of electrons in the valence shell is equal to its group number. For example: Valence electrons in P is 5 and its group number is also 5.
57. Consider the following statements about an element ‘X‘ with number of protons 13.*
(A) It forms amphoteric oxide.
(B) Its valency is three.
(C) The formula of its chloride is XC3.
The correct statements (s) is/are.
(a) only (A)
(b) only (B)
(c) (A) and (C)
(d) (A), (B) and (C)
Ans. (d) (A), (B) and (C)
Explanation :
An element having the protons 13 has the atomic number 13 and the element having the atomic number 13 is Aluminium, it forms the amphoteric oxide which are both acidic and basic in nature and it has the valency 3 and its oxide is of the formula XC3 such as Al2O3.
58. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong ?[NCERT, Exemplar]
(a) Metal
(b) Metalloid
(c) Non-metal
(d) Left-hand side element
Ans. (b) Metalloid
Explanation :
The element will be a metalloid since the elements present in the group 14 have the characteristics of both metals and the non- metals also they have the valence shell electrons as 4 thus, they form the covalent molecules with the other atoms.
59. The modern periodic law is given by…………
(a) Mendeleev
(b) Einstein
(c) Bohr
(d) Mosley
Ans. (d) Mosley
Explanation :
The modern periodic law was given by Henry Mosley and his periodic table was based on the fact that “The physical and chemical properties of the elements are periodic functions of their atomic numbers”. The atomic number is equal to the number of electrons or protons in a neutral atom.”60. Which one of the following property does not increase while moving down the group in the periodic table ?
(a) Atomic radius
(b) Metallic character
(c) Valence electrons
(d) Number of shells in an element
Ans. (c) Valence electrons
Explanation :
The number of valence electrons does not increase while moving down the group in the periodic table.
61. On moving from left to right in a period in the periodic table, the size of the atom: [NCERT, Exemplar]
(a) increases
(b) decreases
(c) does not change appreciably
(d) first decreases and then increases
Ans. (b) decreases
Explanation :
On moving from left to right in a period, the atomic size decreases as the atomic number (i.e., the number of protons and electrons) increases but the number of shells remain the same. Therefore, the force of attraction between the nucleus and the outermostshell of electrons (effective nuclear charge) increases, thus leading to a decrease in the size.
62. A liquid non-metal is ……………
(a) phosphorous
(b) mercury
(c) bromine
(d) nitrogen
Ans. (c) bromine
Explanation :
Bromine is the liquid non- metal present in the group 17 of the Periodic table.
63. The period that contains only gaseous elements are:
(a) 1
(b) 2
(c) 3
(d) 4
Ans. (a) 1
Explanation :
Period 1 has only gaseous elements namely hydrogen and helium.
64. The pairs of elements with the following atomic numbers have the same chemical properties:
(a) 13 and 12
(b) 3 and 11
(c) 4 and 24
(d) 2 and 1
Ans. (b) 3 and 11
Explanation : The elements with the atomic number 3 and 11 have the same properties because both elements have same valence shell electronic configuration, i.e., ns1.
65. The positions of four elements A, B, C and D in the Modern Periodic Table are shown below. Which element is most likely to form an acidic oxide ?
(a) A
(b) B
(c) C
(d) D
Ans. (c) CExplanation :
From the position of element C in the periodic table, it is clear that it is a non-metal. Therefore C will form the acidic oxide since oxides of non-metals are acidic in nature.
66. Elements P, Q, R and S have atomic numbers 11, 15, 17 and 18 respectively. Which of them are reactive non-metals ?
(a) P and Q
(b) P and R
(c) Q and R
(d) R and S
Ans. (c) Q and R.
Explanation :
We are given that elements P, Q, R and S have atomic numbers 11, 15, 17, and 18. We have to find reactive non metals in given elements. We know that atomic number of sodium = 11
Therefore, P is sodium.
Sodium is metal not non metal.
We know that atomic number of phosphorus, P = 15
Therefore, Q is phosphorus.
It is not a metal because it requires 3 electrons to complete its octet.Atomic number of chlorine = 17
Therefore, element R is chlorine.
It is a non metal since it requires an electron to complete its octet.
Atomic number of argon = 18
Therefore, element S is argon.
It is noble gas because it has completely filled shells. It is non reactive because it does not require any electron to complete its octet.
Hence, Q and R are reactive non metals.
67. Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period ?[NCERT, Exemplar]
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E
Ans. (b) B, C, D.
Explanation :
The first period contains 2 elements. Whereas, both second and third period contains 8 elements. Therefore, the first period contains 1 to 2 atomic number. The second period contains 3 to 10 atomic number. The third contains 11 to 18 atomic number. The fourth period contains 19 to 36 atomic number. Therefore, B, C and D belong to the same period.68. Which pair of elements belong to the same group if elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively.
(a) A and B
(b) B and D
(c) A and C
(d) D and E
Ans. (c) A and C.
Explanation :
Since both A and C elements have the same number of valence electrons which is 7, hence they belong to the same group, i.e. 17th group of the periodic table.
69. _______ element would lose an electron easily ?
(a) Mg
(b) Na
(c) K
(d) Ca
Ans. (d) Ca.
Explanation :
The electronic configuration of calcium is 2, 8, 8, 2. It will lose two electron from its outermost shell because on losing two electrons it will acquire the nearest Nobel gas configuration and will become more stable.70. Which among the following elements has the largest atomic radii ?[NCERT, Exemplar]
(a) Na
(b) Mg
(c) K
(d) Ca
Ans. (d) Ca.
Explanation :
Calcium will have the highest atomic radii since with the increase in the atomic number atomic radii also increases due to the increase in the number of the electronic shells.
71. The correct increasing order of the atomic radii of O, F and N will be:
(a) O, F, N
(b) N, F, O
(c) O, N, F
(d) F, O, N
Ans. (c) O, N, F.
Explanation :
The increasing order of atomic radii is F, O, N as atomic number of F, O and N are 9,8 and 7 respectively and as the atomic number increases the atomic radii also increases due to the increase in the number of the electronic shells.72. Which one of the following elements exhibits maximum number of valence electrons ? [NCERT, Exemplar]
(a) Na
(b) Al
(c) Si
(d) P
Ans. (d) P
Explanation : Valence electrons in Na, Al, Si and P are 1, 3, 4 and 5. Hence, phosphorus has maximum number of valence electrons.
73. The least reactive element in group 17 is…………
(a) Fluorine
(b) Chlorine
(c) Bromine
(d) Iodine
Ans. (d) Iodine.
Explanation :
Iodine is the least reactive element in the group 17 of the periodic table since with the increase in the number of the shells the hold of the nucleus on the electron becomes weak and thus, it is less reactive in nature.
74. Three elements B, Si and Ge are:[NCERT, Exemplar]
(a) metals
(b) non-metals
(c) metalloids
(d) metal, non-metal and metalloid respectively
Ans. (c) metalloids
Explanation :
The elements B, Si and Ge are metalloids since they have the characteristics of both metals and the non-metals also they have the valence shell electrons as 4 and they form the covalent bonds with the other elements.
75. In periodic table, helium is placed at:
(a) top left corner
(b) bottom right corner
(c) bottom left corner
(d) top right corner
Ans. (d) top right corner
Explanation :
Helium is the second element on the periodic table. It is located in period 1 and group 18 or 8A on the right-hand side of the table. This group contains the noble gases, which are the most chemically inert elements on the periodic table. Thus it is placed on the top right corner in the periodic table.76. A factor that affects the ionisation potential of an element is
…………
(a) atomic size
(b) electron affinity
(c) electro-negativity
(d) neutrons
Ans. (a) atomic size
Explanation :
Larger the atomic size, smaller is the ionisation potential. It is due to that the size of atom increases the outermost electrons farther away from the nucleus and nucleus loses the attraction on that electrons and hence can be easily removed and thus it affects the ionisation potential of the atom.
77. Which of the following element forms basic oxide?
(a) Phosphorous
(b) Argon
(c) Chlorine
(d) Potassium
Ans. (d) Potassium
Explanation :
The elements which can donate their valence electrons to other atoms are the metallic elements which form basic oxides as they give hydroxides in their aqueous solutions.
78. Which of the two elements will form covalent bonds?
X = Group 2
Y = Group 14
Z = Group 16
(a) X and Y
(b) Y and Z
(c) Z and A
(d) None of the above
Ans. (b) Y and Z
Explanation :
Covalent bond is formed by elements having less difference in their electronegativity. Since the covalent bond is formed between two non-metal elements. Now, out of X, Y and Z the element Y (of group 14) and element Z of group (16) are non-metals. Thus the elements Y and Z will form covalent bonds.
79. The correct order of decreasing metallic character of elements
Na, Si, Cl, Mg, Al
(a) Cl > Si > Al > Mg > Na.
(b) Na > Mg > Al > Si > Cl
(c) Na > Si > Mg > Al > Cl
(d) Al > Na > Si > Cl > Mg
Ans. (b) Na > Mg > Al > Si > Cl
Explanation :
Sodium has 1, Mg has 2 and Al and 3, Si has 4 electrons in outermost orbits. But Cl has 7 electrons in its outermost orbit. Hence, sodium shows the maximum character of metallic elements, and chlorine shows the character of a non-metallic elements. Electropositive elements are metallic in character.
80. The positions of four elements A, B, C and D in the modern periodic table are shown below.
The correct order of increasing order of atomic size is:
(a) C < B < D < A
(b) A < B < C < D
(c) B < C < A < D
(d) D < C < B < A
Ans. (a) C < B < D < A
Explanation :
Atomic size decreases along a period and increases down the group.
81. As we move down the group, the number of shells:
(a) increases
(b) decreases
(c) remain Same
(d) none of the above
Ans. (a) increases
Explanation :
As we move down in the group ,number of shells increases. Hence, size of the atom also increases.
82. The commonly used unit of atomic radii is:
(a) angstrom
(b) meters
(c) millimetres
(d) centimetres
Ans. (a) angstrom
Explanation :
Atomic radius is usually expressed in Angstrom units. It is because the size of atom is very small. It is equivalent to 1×10−10metres.
83. Nuclear charge is directly proportional to the:
(a) number of electrons
(b) number of neutrons
(c) number of protons(d) number of nucleons
Ans. (c) number of protons
Explanation :
Protons and neutrons are present in the nucleus and both are collectively called nucleons. Protons are charged particles and neutrons are neutral or do not have any charge on them. So ,thetotal charge on the nucleus is due to the number of protons present in the nucleus.
84. What happens to the nuclear charge as we move down the group in a periodic table?
(a) Increases
(b) Decreases
(c) Remains the same
(d) None of the above
Ans. (a) Increases
Explanation :
Nuclear charge is a function of the number of protons present in an atom. If we move from right to left or from top to bottom in a periodic table we can always observe an increase in the number of protons as there is an increase in the number of electrons.
85. The maximum amount of energy required to remove the most loosely bounded electron from an isolated,neutral, gaseous atom is known as:
(a) electron Affinity
(b) ionisation energy
(c) electro negativity
(d) none of the above
Ans. (b) ionisation energy
Explanation :
Ionization Energy is the amount of energy required to remove an electron from an isolated atom or molecule.
86. Which of the following elements has the highest electro negativity?
(a) Fluorine
(b) Oxygen
(c) Boron
(d) Beryllium
Ans. (a) Fluorine
Explanation :
The electro negativity values for the VIIA group or Halogen value are the highest in their period or row, and decreases as the atomic number of the Halogen increases.The group VIIA /17 or Halogens have a valance electron configuration of 2, 8, 7. This gives the Halogens 7 valance electrons. The electron configuration causes the Halogens to have a strong pull for one more electron. The definition of electronegativity is the pull of the element for more electrons. Thus the VIIA or Halogens will have the highest electronegativity of any element intheir row, or period.
87. Which of the following has the highest atomic size?
(a) Magnesium
(b) Sodium
(c) Sulphur
(d) Chlorine
Ans. (b) Sodium
Explanation :
Sodium ,Magnesium, Sulphur and Chlorine belongs to the third period. For elements of same period, size decreases while going from left to rightacross a period
88. Which of the following alkali metals is radioactive in nature?
(a) Potassium
(b) Rubidium
(c) Caesium
(d) Francium
Ans. (d) Francium
Explanation :
Francium is the second rarest element on the earth. It has a half - life of about 22 minutes only. It is used in cancer diagnostics , spectroscopic experiments, etc.
89. Which of the following has zero electron affinity?
(a) Halogens
(b) Alkali metals
(c) Alkaline earth metals
(d) Noble gases
Ans. (d) Noble gases
Explanation :
Noble gases have zero electron affinity due to stable electronic configuration.
90. Which of the following is the correct order of the atomic radii of the elements oxygen, fluorine and nitrogen?
(a) O < F < N
(b) N < F < O
(c) O < N < F
(d) F < O < N
Ans. (d) F < O < N
Explanation :
Oxygen (8), fluorine (9) and nitrogen (7) belong to the same period of the periodic table, in the order nitrogen, oxygen and fluorine. Now in a period, on moving from left to right the atomic radius of the elements decreases. Therefore, the atomic radius of nitrogen is the largest.
91. Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the samegroup of the Periodic Table as
(a) Na
(b) Mg
(c) Al
(d) Si
Ans. (b) Mg
Explanation :
Group 2 alkaline earth metal atoms have two valence electrons each. They can donate their two valence electrons to two other chlorine atoms to form the solid compounds of the form XCl2.This XCl2 compound being ionic in nature, has a very strong electrostatic force of attraction between 2 chloride ions and 1 metal ion. Thus, a large amount of heat is required to break these strong bonds, causing the compounds to have very high melting and boiling points.
92. Out of Li and Be which has higher ionisation energy?
(a) Li
(b) Be
(c) Both have same
(d) None
Ans. (a) Li
Explanation :
Ionization Potential is the amount of energy required to removethe electron from an atom. It is also known as Ionization energy. Ionization energy increases across the period with increase in atomic number. Li and Be belongs to the same period having electronic configuration 2,1 and 2,2 respectively. Hence Be will have more ionization energy tan Li.
93. Observe the following table:
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