JEE Chemistry Classification of Elements and Periodicity in Properties MCQs Set 12

Chemistry Objective Questions and Answers: Classification Of Elements and Periodicity In Properties

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Multiple Choice Questions

Question 1: Uranium (Z = 92) is the last natural element in the periodic table. If the periodic table is taken up to Z = 112, the total number of transuranic elements is:
(a) 21
(b) 20
(c) 11
(d) 12
Show Answer & Explanation

Answer: (b) 20

Explanation:
1. Transuranic elements have Z greater than 92.
2. Up to Z = 112 these are 93 to 112, which is 20 elements.

Teacher's Note:
1. Count the shells and valence electrons to find period and group. The block is decided by the subshell that receives the last electron.
2. Revise the trend with two or three examples.

Question 2: Which two elements are in same period as well as same group of modern periodic table:
(a) Z = 23, Z = 31
(b) Z = 65, Z = 66
(c) Z = 52, Z = 87
(d) Z = 58, Z = 46
Show Answer & Explanation

Answer: (b) Z = 65, Z = 66

Explanation:
1. Z = 65 (Tb) and Z = 66 (Dy) are both lanthanides in group 3 and the 6th period.

Teacher's Note:
1. Count the shells and valence electrons to find period and group. The block is decided by the subshell that receives the last electron.
2. Revise the trend with two or three examples.

Question 3: Which of the following statements is not correct for the element with the electronic configuration 1s², 2s² 2p⁶, 3s² 3p⁶ 3d¹⁰, 4s² 4p⁶ 4d¹⁰ 4f¹⁴, 5s² 5p⁶ 5d¹⁰, 6s²?
(a) It belongs to group IIB and the 6th period
(b) It is liquid at room temperature
(c) It is a transition element
(d) It is used in thermometers
Show Answer & Explanation

Answer: (c) It is a transition element

Explanation:
1. The configuration ends with 6s² 5d¹⁰ 4f¹⁴, which is mercury (Z = 80).
2. Hg is in group 12 and the 6th period, and is a liquid used in thermometers.
3. Zn, Cd and Hg have filled d10 shells and are not counted as transition elements, so statement (3) is not correct.

Teacher's Note:
1. Count the shells and valence electrons to find period and group. The block is decided by the subshell that receives the last electron.
2. Revise the trend with two or three examples.

Question 4: The general electronic configuration of the outermost and penultimate shells is (n – 1)s² (n – 1)p⁶ (n – 1)dˣ ns². If n = 4 and x = 5, the number of protons in the nucleus will be:
(a) > 25
(b) < 24
(c) 25
(d) 30
Show Answer & Explanation

Answer: (c) 25

Explanation:
1. n = 4, x = 5 gives 3s² 3p⁶ 3d⁵ 4s² with 25 electrons.
2. The atom is Mn, so there are 25 protons.

Teacher's Note:
1. Count the shells and valence electrons to find period and group. The block is decided by the subshell that receives the last electron.
2. Revise the trend with two or three examples.

Question 5: An ion M³⁺ h as electronic con figuration [Ar] 3d¹⁰ 4s² element M belongs to:
(a) s-block
(b) p-block
(c) d-block
(d) f-block
Show Answer & Explanation

Answer: (b) p-block

Explanation:
1. M³⁺ has the configuration [Ar] 3d¹⁰ 4s², which is 30 electrons.
2. So the neutral atom has 33 electrons and is arsenic.
3. Arsenic is a p-block element.

Teacher's Note:
1. Count the shells and valence electrons to find period and group. The block is decided by the subshell that receives the last electron.
2. Revise the trend with two or three examples.

Question 6: What is the atomic number of element having maximum no. of unpaired e– in 4p subshell:
(a) 33
(b) 17
(c) 53
(d) 15
Show Answer & Explanation

Answer: (a) 33

Explanation:
1. The 4p subshell has three unpaired electrons when it is 4p³.
2. This is arsenic (Z = 33).

Teacher's Note:
1. Count the shells and valence electrons to find period and group. The block is decided by the subshell that receives the last electron.
2. Revise the trend with two or three examples.

Question 7: According to Slater rule, Effective nuclear charge in group generally:
(a) Increases down the group
(b) Decreases down the group
(c) Remains constant
(d) First increases then decreases
Show Answer & Explanation

Answer: (c) Remains constant

Explanation:
1. By Slater's rules Zeff of the outer electron stays almost the same down a group.
2. The increase in nuclear charge is cancelled by the added shielding.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 8: In sodium atom the screening is due to:
(a) 3s², 3p⁶
(b) 2s¹
(c) 1s², 2s², 2p⁶
(d) 1s², 2s²
Show Answer & Explanation

Answer: (c) 1s², 2s², 2p⁶

Explanation:
1. The outer 3s electron of Na is screened by the inner 1s², 2s² and 2p⁶ electrons (10 electrons).

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 9: If the difference in atomic size of : Na⁻ Li = x; Rb⁻ K = y; Fr⁻ Cs = z Then correct order will be:
(a) x = y = z
(b) x > y > z
(c) x < y < z
(d) x < y << z
Show Answer & Explanation

Answer: (b) x > y > z

Explanation:
1. Radii: Li 152, Na 186, K 227, Rb 248, Cs 265, Fr 270 pm.
2. x = 34, y = 21 and z = 5, so x > y > z.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 10: Which of the following order of radii is correct?
(a) Li < Be < Mg
(b) H⁺ < Li⁺ < H⁻
(c) O < F < Ne
(d) Na⁺ > F⁻ > O²⁻
Show Answer & Explanation

Answer: (b) H⁺ < Li⁺ < H⁻

Explanation:
1. H⁺ is just a proton, Li⁺ is small and H⁻ is large, so H⁺ < Li⁺ < H⁻.
2. The other orders are wrong. For example Li is larger than Be, and F⁻ is larger than Na⁺.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 11: K⁺, Ar, Ca²⁺ and S²⁻ contains _:
(a) Same electronic configuration and atomic volume
(b) Different electronic configuration but same IP.
(c) Same electronic configuration but different atomic volume
(d) None
Show Answer & Explanation

Answer: (c) Same electronic configuration but different atomic volume

Explanation:
1. K⁺, Ar, Ca²⁺ and S²⁻ all have 18 electrons (same configuration).
2. The nuclear charges differ, so their sizes are different.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 12: Which of the following is not an isoelectronic series?
(a) Cl , P³⁻, Ar
(b) N³⁻, Ne, Mg²⁺ —
(c) B , He, Li³⁺ +
(d) N³⁻, S²⁻, Cl
Show Answer & Explanation

Answer: (d) N³⁻, S²⁻, Cl

Explanation:
1. N³⁻ and S²⁻ are not isoelectronic: N³⁻ has 10 electrons and S²⁻ and Cl⁻ have 18.
2. The other sets have equal electron numbers.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 13: Which group of atoms have nearly same atomic radius:
(a) Na, K, Rb, Cs
(b) Li, Be, B, C
(c) Fe, Co, Ni
(d) F, Cl, Br, I
Show Answer & Explanation

Answer: (c) Fe, Co, Ni

Explanation:
1. d-block elements like Fe, Co and Ni have nearly the same radius, because added electrons go to the inner d subshell and screening compensates the charge.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 14: Atomic radii of Fluorine and Neon in Angstrom units are given by:
(a) 0.72, 1.60
(b) 1.60, 1.60
(c) 0.72, 0.72
(d) None of these
Show Answer & Explanation

Answer: (a) 0.72, 1.60

Explanation:
1. The covalent radius of F is 0.72 A, while Ne has only a van der Waals radius of 1.60 A.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 15: Which of the following has largest radius:
(a) 1s² 2s² 2p⁶ 3s²
(b) 1s² 2s² 2p⁶ 3s² 3p¹
(c) 1s² 2s² 2p⁶ 3s² 3p³
(d) 1s² 2s² 2p⁶ 3s² 3p⁵
Show Answer & Explanation

Answer: (a) 1s² 2s² 2p⁶ 3s²

Explanation:
1. The four are Mg, Al, P and Cl of the same period.
2. Radius decreases across the period, so Mg (3s²) is the largest.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 16: Which of the following order of atomic/ionic radius is not correct:
(a) I⁻ > I > I⁺
(b) Mg²⁺ > Na⁺ > F⁻
(c) P⁵⁺ < P³⁺
(d) Li > Be > B
Show Answer & Explanation

Answer: (b) Mg²⁺ > Na⁺ > F⁻

Explanation:
1. Isoelectronic ions decrease in size as nuclear charge rises: F⁻ > Na⁺ > Mg²⁺.
2. So the order Mg²⁺ > Na⁺ > F⁻ is wrong.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 17: The radius of potassium atom is 0.203 nm. The radius of the potassium ion in nanometer will be:
(a) 0.133
(b) 0.231
(c) 0.234
(d) 0.251
Show Answer & Explanation

Answer: (a) 0.133

Explanation:
1. A cation is smaller than its atom as the outer shell is lost and Zeff increases.
2. So K⁺ is smaller than 0.203 nm, which gives 0.133 nm.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 18: S²⁻ is not isoelectronic with:
(a) Ar
(b) Cl⁻
(c) HS⁻
(d) Ti³⁺
Show Answer & Explanation

Answer: (d) Ti³⁺

Explanation:
1. S²⁻ has 18 electrons, like Ar, Cl⁻ and HS⁻.
2. Ti³⁺ has 19 electrons, so it is not isoelectronic.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 19: The best reason to account for the general tendency of atomic diameters to decrease as the atomic numbers increase within a period of the periodic table is the fact that:
(a) Outer electrons repel inner electrons
(b) Closer packing among the nuclear particles is achieved
(c) The number of neutrons increases
(d) The increasing nuclear charge exerts a greater attractive force on the electrons
Show Answer & Explanation

Answer: (d) The increasing nuclear charge exerts a greater attractive force on the electrons

Explanation:
1. Across a period electrons are added to the same shell while nuclear charge rises.
2. The stronger pull of the nucleus contracts the atom.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 20: In an anion:
(a) Number of proton decreases
(b) Protons are more than electrons
(c) Effective nuclear charge is more
(d) Radius is larger than neutral atom
Show Answer & Explanation

Answer: (d) Radius is larger than neutral atom

Explanation:
1. An anion has more electrons than protons, so Zeff is lower and the electron cloud expands.
2. Hence the radius is larger than that of the neutral atom.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 21: Which of the following ion has largest size:
(a) F⁻
(b) Al³⁺
(c) Cs⁺
(d) O²⁻
Show Answer & Explanation

Answer: (c) Cs⁺

Explanation:
1. Cs⁺ has radius about 167 pm, bigger than O²⁻ (140 pm), F⁻ (133 pm) and Al³⁺ (50 pm).

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 22: Spot the incorrect order of atomic radii:
(a) r(Cu) > r(Zn)
(b) r(Cl) > r(F)
(c) r(P) > r(S)
(d) r(Sc) > r(Ti)
Show Answer & Explanation

Answer: (a) r(Cu) > r(Zn)

Explanation:
1. Zn (134 pm) is larger than Cu (128 pm) because of electron-electron repulsions, so rCu > Zn is incorrect.
2. The other orders are true.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 23: Which electronic configuration of an atom is smallest in size:
(a) 3s²
(b) 3s² 3p³
(c) 3s¹
(d) 3s² 3pₓ² 3p_y¹ 3p_z¹
Show Answer & Explanation

Answer: (d) 3s² 3pₓ² 3p_y¹ 3p_z¹

Explanation:
1. The configuration 3s² 3p²x 3p¹y 3p¹z is sulphur (3p⁴).
2. Radius decreases across the third period, so S is smaller than Na, Mg and P.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 24: The covalent and vander Waal's radii of hydrogen respectively are:
(a) 0.37 Å, 1.2 Å
(b) 0.37 Å, 0.37 Å
(c) 0.8 Å, 0.8 Å
(d) 0.8 Å, 0.37 Å
Show Answer & Explanation

Answer: (a) 0.37 Å, 1.2 Å

Explanation:
1. The covalent radius of hydrogen is 37 pm (0.37 A) and the van der Waals radius is much larger, about 1.2 A.

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

Question 25: Which of the following sequence is correct for decreasing order of ionic radius:
(a) Se²⁻, I⁻, Br⁻, O²⁻, F⁻
(b) I⁻, Se²⁻, O²⁻, Br⁻, F⁻
(c) Se²⁻, I⁻, Br⁻, F⁻, O²⁻
(d) I⁻, Se²⁻, Br⁻, O²⁻, F⁻
Show Answer & Explanation

Answer: (d) I⁻, Se²⁻, Br⁻, O²⁻, F⁻

Explanation:
1. Ionic radii: I⁻ (216 pm) > Se²⁻ (198) > Br⁻ (196) > O²⁻ (140) > F⁻ (133).

Teacher's Note:
1. Compare shells first, then nuclear charge. For isoelectronic ions, the larger nuclear charge gives the smaller radius.
2. Revise the trend with two or three examples.

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