MCQs on Class 11 Chemistry Chapter 2 | Structure of Atom MCQs for NEET 2021

(1) Chlorine exists in two isotopic forms, Cl-37 and Cl-35 but its atomic mass is 35.5. This indicates the ratio of Cl-37 and Cl-35 is approximately

[A] 1:2

[B] 1:1

[C] 1:3

[D] 3:1

Answer: 1:3

(2) Total number of orbitals associated with third shell will be __________.

[A] 2

[B] 4

[C] 9

[D] 3

Answer: 9

(3) Two atoms are said to be isobars if.

[A] they have same atomic number but different mass number.

[B] they have same number of electrons but different number of neutrons.

[C] they have same number of neutrons but different number of electrons.

[D] sum of the number of protons and neutrons is same but the number of protons is different.

Answer: sum of the number of protons and neutrons is same but the number of protons is different.

(4) Which of the following properties of atom could be explained correctly by Thomson Model of atom?

[A] Overall neutrality of atom.

[B] Spectra of hydrogen atom.

[C] Position of electrons, protons and neutrons in atom.

[D] Stability of atom.

Answer: Overall neutrality of atom.

(5) Which of the following statements about the electron is incorrect?

[A] It is a negatively charged particle.

[B] The mass of electron is equal to the mass of neutron.

[C] It is a basic constituent of all atoms.

[D] It is a constituent of cathode rays.

Answer: The mass of electron is equal to the mass of neutron.

(6) Which of the following statement is not correct about the characteristics of cathode rays?

[A] They start from the cathode and move towards the anode.

[B] They travel in straight line in the absence of an external electrical or magnetic field.

[C] Characteristics of cathode rays do not depend upon the material of electrodes in cathode ray tube.

[D] Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube.

Answer: Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube.

(7) The probability density plots of 1s and 2s orbitals are given in Fig

The density of dots in a region represents the probability density of finding electrons in the region.

On the basis of above diagram which of the following statements is incorrect?

[A] 1s and 2s orbitals are spherical in shape.

[B] The probability of finding the electron is maximum near the nucleus.

[C] The probability of finding the electron at a given distance is equal in all directions.

[D] The probability density of electrons for 2s orbital decreases uniformly as distance from the nucleus increases.

Answer: The probability density of electrons for 2s orbital decreases uniformly as distance from the nucleus increases.

(8) Which of the following options does not represent ground state electronic configuration of an atom?

[A] 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸ 4s²

[B] 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4s²

[C] 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

[D] 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹

Answer: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4s²

(9) Which of the following conclusions could not be derived from Rutherford’s α -particle scattering experiment?

[A] Most of the space in the atom is empty.

[B] The radius of the atom is about 10–10 m while that of nucleus is 10–15 m.

[C] Electrons move in a circular path of fixed energy called orbits.

[D] Electrons and the nucleus are held together by electrostatic forces of attraction.

Answer: Electrons move in a circular path of fixed energy called orbits.

(10) In which of the following pairs, the ions are iso-electronic?

[A] Na⁺, Mg²⁺

[B] Al³⁺, O^–

[C] Na⁺, O^2-

[D] N3^–, Cl^–

Answer: C, D

(11) Maximum number of electrons in a subshell with l = 3 and n = 4 is

[A] 10

[B] 12

[C] 14

[D] 16

Answer: 14

(12) The correct set of four quantum numbers for the valence electron of rubidium atom (Z = 37) is

[A] 5, 0, 0, + 1/2

[B] 5, 1, 0, + 1/2

[C] 5, 1, 1, + 1/2

[D] 6, 0, 0, + 1/2

Answer: 5, 0, 0, + 1/2

(13) Identify the wrong statement in the following

[A] Atomic radius of the elements increases as one moves down the first group of the periodic table

[B] Atomic radius of the elements decreases as one moves across from left to right in the 2nd period of the

[C] Amongst isoelectronic species, smaller the positive charge on the cation, smaller is the ionic radius

[D] Amongst isoelectronic species, greater the negative charge on the anion, larger is the ionic radius

Answer: Amongst isoelectronic species, smaller the positive charge on the cation, smaller is the ionic radius

(14) A gas absorbs a photon of 355 nm and emits at two wavelengths. If one of the emissions is at 680 nm, the other is at: [AIEEE 2011]

[A] 518 nm

[B] 1035 nm

[C] 325 nm

[D] 743 nm

Answer: 743 nm

(15) The energy of an electron in first Bohr orbit of H-atom is –13.6 eV. The possible energy value of electron in the excited state of Li²⁺ is [West Bengal JEE 2011]

[A] – 122.4 eV

[B] 30.6 eV

[C] – 30.6 eV

[D] 13.6 eV

Answer: – 30.6 eV

(16) The electronic transitions from n = 2 to n = 1 will produce shortest wavelength in (where n = principal quantum state) [West Bengal JEE 2011]

[A] Li⁺²

[B] He⁺

[C] H

[D] H⁺

Answer: Li⁺²

(17) The energy required to break one mole of Cl – Cl bonds in Cl₂ is 242 kJ mol^–1. The longest wavelength of light capable of breaking a single Cl – Cl bond is

(c = 3×108 ms^–1 and NA = 6.02×1023 mol^–1)

[A] 594 nm

[B] 640 nm

[C] 700 nm

[D] 494 nm

Answer: 494 nm

(18) Mg²⁺ is isoelectronic with

[A] Ca²⁺

[B] Na⁺

[C] Zn²⁺

[D] Cu²⁺

Answer: Na⁺

(19) Which one of the following sets of ions represents a collection of isoelectronic species?

[A] K⁺, Cl^–, Ca²⁺, Sc³⁺

[B] Ba²⁺, Sr²⁺, K⁺, S^2–

[C] N^3–, O^2–, F^–, S^2–

[D] Li⁺, Na⁺, Mg²⁺, Ca²⁺

Answer: K⁺, Cl^–, Ca²⁺, Sc³⁺

(20) Consider the ground state of Cr atom (Z = 24). The numbers of electrons with the azimuthal quantum numbers, l = 1 and 2 are, respectively: [AIEEE 2004]

[A] 12 and 4

[B] 12 and 5

[C] 16 and 4

[D] 16 and 5

Answer: 12 and 5

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