Chemistry MCQs for Class 11 Chapter 2 Structure of Atom

Q.1. Number of protons, neutrons and electrons in the element ₈₉X²³¹ is
(a) 89, 89, 242
(b) 89, 142, 89
(c) 89, 71, 89
(d) 89, 231, 89

Answer

(b) Number of p = number of e– = 89 and neutrons 231 – 89 = 142.

Q.2. Atoms with same mass number but different atomic numbers are called
(a) isotopes
(b) isobars
(c) isochores
(d) None of these

Answer

(b) Atoms with mass number but different atomic numbers are called isobars.

Q.3. The increasing order (lowest first) for the values of e/m (charge/mass) for
(a) e, p, n, α
(b) n, p, e, α
(c) n, p, α, e
(d) n, α, p, eAnswer

Answer

(d) n, α, p, e Explanation:
(i) (e/m) for (i) neutron = (01) = 0 (ii) α− particle = (24) = 0.5 (iii) Proton = (11) = 1 (iv) electron = (11837) = 1837.

Q.4. The energy of second Bohr orbit of the hydrogen atom is -328 kJ mol-1; hence the energy of fourth Bohr orbit would be:
(a) -41 kJ mol^-1
(b) -82 kJ mol^-1
(c) -164 kJ mol^-1
(d) -1312 kJ mol^-1

Answer

(b)

Q.5. The ionisation potential of a hydrogen atom is –13.6 eV. What will be the energy of the atom corresponding to n = 2.
(a) – 3.4 eV
(b) – 6.8 eV
(c) – 1.7 eV
(d) –2.7 eV

Answer

(a)

Q.6. The ionization enthalpy of hydrogen atom is 1.312 × 10⁶ J mol^-1. The energy required to excite the electron in the atom from n = 1 to n = 2 is
(a) 8.51 × 10⁵ J mol^-1
(b) 6.56 × 10⁵ J mol^-1
(c) 7.56 × 10⁵ J mol^-1
(d) 9.84 × 10⁵ J mol^-1

Answer

Answer: (d) 9.84 × 10⁵ J mol^-1
Energy required when an electron makes transition from n = 1 to n = 2
E₂=−(1.312 × 10⁶ × (1)²)/(2²)
= −3.28 × 10⁵ J mol^-1
E₁ = −1.312 × 10⁶ J mol^-1
ΔE = E₂ − E₁
=−3.28 × 10⁵−(−13.2 × 10⁶)
ΔE = 9.84×10⁵ J mol^-1

Q.7. In which of the following Bohr’s stationary state, the electron will be at maximum distance from the nucleus ?
(a) IInd
(b) Ist
(c) Vth
(d) IIIrd

Answer

(c)

Q.8. For a given principal level n = 4, the energy of its subshells is in the order
(a) s < p < d < f
(b) s > p > d > f
(c) s < p < f < d
(d) f < p < d < s

Answer

(a)

Q.9. 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:
(a) 518 nm
(b) 1035 nm
(c) 325 nm
(d) 743 nm

Answer

Answer: (d) 743 nm
Explanation:
From Law of Conservation of energy, energy of absorbed photon must be equal to combined energy of two emitted photons.
ET = E₁ + E₂ ….. (1)
Where E₁ is Energy of first emitted photon emitted and E₂is Energy of second emitted photon.
Energy E and wavelength λ of a photon are related by the equation
E= (hc)/ (λ)….. (2)
Where Plancks constant = h, c is velocity of light.
Substituting the values from (2) in (1) we get
(hc/λ_T) = (hc)/ (λ₁) + (hc)/ (λ₂)
Or (1λ𝑇) = (1λ1) + (1λ2) …… (3)
Substituting given values in (3) we get
(1355) = (1680) + (1λ2)
Or (1)(λ𝑇) = (1355) − (1680)
⇒ (1λ2) = (680 − 355)/ (355 × 680)
⇒ λ₂ = 742.77nm

Q.10. Which of the following statements do not form a part of Bohr’s model of hydrogen atom ?
(a) Energy of the electrons in the orbits are quantized
(b) The electron in the orbit nearest the nucleus has the lowest energy
(c) Electrons revolve in different orbits around the nucleus
(d) The position and velocity of the electrons in the orbit cannot be determined simultaneously.

Answer

(d) Uncertainty principle which was given by Heisenberg and not Bohr’s postulate.

Q.11. Which of the following statements in relation to the hydrogen atom is correct?
(a) 3s orbital is lower in energy than 3p orbital
(b) 3p orbital is lower in energy than 3d orbital
(c) 3s and 3p orbitals are of lower energy than 3d orbital
(d) 3s, 3p and 3d orbitals all have the same energyAnswer

Answer

(d) 3s, 3p and 3d orbitals all have the same energy
A hydrogen atom has 1st configuration and these its, 3p and 3d orbitals will have same energy wrt 1s orbital.

Q.12. The magnetic quantum number specifies
(a) Size of orbitals
(b) Shape of orbitals
(c) Orientation of orbitals
(d) Nuclear Stability

Answer

(c) Orientation of orbitals
The magnetic quantum number specifies orientation of orbitals.

Q.13. If electron, hydrogen, helium and neon nuclei are all moving with the velocity of light, then the wavelength associated with these particles are in the order
(a) Electron > hydrogen > helium > neon
(b) Electron > helium > hydrogen > neon
(c) Electron < hydrogen < helium < neon
(d) Neon < hydrogen < helium < electron

Answer

(a)

Q.14. The electronic configuration of silver atom in ground state is
(a) [Kr]3d¹⁰4s¹
(b) [Xe]4f¹⁴5d¹⁰6s¹
(c) [Kr]4d¹⁰5s¹
(d) [Kr]4d⁹5s²Answer

Answer

(c) [Kr]4d¹⁰5s¹
The electronic configuration of Ag in ground state is [Kr]4d¹⁰5s¹

Q.15. Which of the following element has least number of electrons in its M-shell?
(a) K
(b) Mn
(c) Ni
(d) ScAnswer

Answer

(a) K
K = 19 = 1s²2s²2p⁶3s²3p⁶s¹
3s²3p⁶ = m-shell
= k has only 8 electrons in M shell

Q.16. Which one of the following sets of ions represents a collection of isoelectronic species? (Atomic nos.: F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21)
(a) K⁺, Ca²⁺, Sc³⁺, Cl^–
(b) Na⁺, Ca²⁺ , Sc³⁺, F^–
(c) K⁺, Cl^–, Mg²⁺, Sc³⁺
(d) Na⁺, Mg²⁺, Al³⁺, Cl^–Answer

Answer

(a) K⁺, Ca²⁺, Sc³⁺, Cl^–
Isoelectronic species are those which have same number of electrons.
K⁺ = 19 – 1 = 18; Ca²⁺ = 20 – 2 = 18; Sc³⁺ = 21 – 3 = 18; Cl^– = 17 + 1 = 18
Thus all these ions have 18 electrons in them.

Q.17. The total number of electrons that can be accommodated in all orbitals having principal quantum number 2 and azimuthal quantum number 1 is
(a) 2 (b) 4
(c) 6 (d) 8

Answer

(c) n = 2, l = 1 means 2p–orbital. Electrons that can be accommodated = 6 as p sub-shell has 3 orbital and each orbital contains 2 electrons.

Q.18. In the ground state, an element has 13 electrons in its M-shell. The element is_____.
(a) Copper
(b) Chromium
(c) Nickel
(d) Iron

Answer

(b) Chromium
M shell means it is third shell ⇒ n = 3
Number of electrons in M shell = 13
⇒ 3s²3p⁶3d⁵
The electronic configuration is: (1s²) (2s² 2p⁶) (3s² 3p⁶ 3d⁵) (4s¹)
The element is chromium is Cr.

Q.19. The electrons of the same orbitals can be distinguished by
(a) Principal quantum number
(b) Azimuthal quantum number
(c) Spin quantum number
(d) Magnetic quantum number

Answer

(c) Spin quantum number
Electrons occupying the same orbital are distinguished by Spin quantum number. For spin Quantum number it has two values +1/2 or -1/2,
Hence the value of n, l , m are same for the two electrons occupying in the same orbitals, but only the is different, which is Therefore, Spin quantum number explains the direction through which the electron spins in an orbital. so obviously there are only 2 possible directions. Which is either clockwise or anticlockwise.
So the electron which are available in the same orbitals, must have opposite spins. Hence spin quantum number distinguished b/w the two electrons.

Q.20. What will be the sum of all possible values of l and m for n = 5 ?
(a) 12
(b) 13
(c) 4
(d) 9

Answer

(b)

Q.21. Consider the ground state of Cr atom (Z = 24). The numbers of electrons with the azimuthal quantum numbers, l = 1 and 2 are, respectively:
(a) 12 and 4
(b) 12 and 5
(c) 16 and 4
(d) 16 and 5

Answer

(b) 12 and 5
₂₄Cr → 1s² 2s²2p⁶ 3s² 3p⁶ 3d⁵ 4s¹
As we know for p, l = 1 and d, l = 2
For l = 1, total number of electrons = 12 [2p⁶ and 3p⁶]
For l = 2, total number of electrons = 5 [3d⁵]

Q.22. A body of mass 10 mg is moving with a velocity of 100 ms^-1. The wavelength of de-Broglie wave associated with it would be (Note: h = 6.63 × 10^-34 Js)
(a) 6.63 × 10^-37 m
(b) 6.63 × 10^-31 m
(c) 6.63 × 10^-34 m
(d) 6.63 × 10^-35 m

Answer

(b) 6.63 × 10^-31 m
m = 10 mg
= 10 × 10^-6 kg
v = 100 ms^-1
λ = (ℎ)(𝑚𝑣)
= (6.63×10^-34)/ (10 × 10^-6 × 100)
= 6.63 × 10^-31 m

Q.23. The orbitals are called degenerate when
(a) they have the same wave functions
(b) they have the same wave functions but different energies
(c) they have different wave functions but same energy
(d) they have the same energy

Answer

(d)

Q.24. The ionization enthalpy of hydrogen atom is 1.312 × 10⁶ J mol^-1. The energy required to excite the electron in the atom from n = 1 to n = 2 is
(a) 8.51 × 10⁵ J mol^-1
(b) 6.56 × 10⁵ J mol^-1
(c) 7.56 × 10⁵ J mol^-1
(d) 9.84 × 10⁵ J mol^-1Answer

Answer

(d) 9.84 × 10⁵ J mol^-1
Energy required when an electron makes transition from n = 1 to n = 2
E₂ = −(1.312 × 10⁶ × (1)²)/(2²)
= −3.28 × 10⁵ J mol^-1
E₁ = −1.312 × 10⁶ J mol^-1
ΔE = E₂ − E₁
= −3.28 × 10⁵−(−13.2 × 10⁶)
ΔE = 9.84 × 10⁵ J mol^-1

Q.25. In Hydrogen atom, energy of first excited state is – 3.4 eV. Then find out KE of same orbit of Hydrogen atom
(a) 3.4 eV
(b) 6.8 eV
(c) -13.6 eV
(d) +13.6 eV

Answer

(a) 3.4 eV
For hydrogen atom, The kinetic energy is equal to the negative of the total energy. And the potential energy is equal to the twice of the total energy. The first excited state energy of orbital = -3.4 eV and The kinetic energy of same orbital = -(-3.4 eV) = 3.4 eV Therefore, the kinetic energy of same orbit of hydrogen atom is 3.4 eV.

Q.26. Which of the following sets of quantum numbers represents the highest energy of an atom?
(a) n = 3, l = 0, m = 0, s = + 12
(b) n = 3, l = 1, m = 1, s = + 12
(c) n = 3, l = 2, m = 1, s = + 12
(d) n = 4, l = 0, m = 0, s = + 12

Answer

(c) n = 3, l = 2, m = 1, s = + 12
Explanation:
n = 3, l = 0 represents 3s orbital n = 3, l = 1 represents 3p orbital n = 3, l = 2 represents 3d orbital n = 4, l = 0 represents 4s orbital The order of increasing energy of the orbitals is 3s < 3p < 4s < 3d.

Q.27. In the Bohr’s model of the hydrogen atom, the ratio of the kinetic energy to the total energy of the electron in a quantum state n is:
(a) 1
(b) 2
(c) -1
(d) -2

Answer

(c)

Q.28. The number of spherical nodes in 3p orbitals are
(a) one
(b) three
(c) two
(d) None of these

Answer

(a)

Q.29. Which of the following statements does not form a part of Bohr’s model of hydrogen atom?
(a) Energy of the electrons in the orbit is quantised.
(b) The electron in the orbit nearest the nucleus has the lowest energy
(c) Electrons revolve in different orbits around the nucleus
(d) The position and velocity of the electrons in the orbit cannot be determined simultaneously

Answer

(d) The position and velocity of the electrons in the orbit cannot be determined simultaneously
Explanation:
The position and velocity of electrons cannot be determined simultaneously does not fit in with the Bohr’s model of H atom. It is a part of Heisenberg’s uncertainty principle

Q.30. Which of the following statements in relation to the hydrogen atom is correct?
(a) 3s orbital is lower in energy than 3p orbital
(b) 3p orbital is lower in energy than 3d orbital
(c) 3s and 3p orbitals are of lower energy than 3d orbital
(d) 3s, 3p and 3d orbitals all have the same energy.

Answer

(d) 3s, 3p and 3d orbitals all have the same energy
Explanation:
A hydrogen atom has 1s1 configuration and these its, 3p and 3d orbitals will have same energy wrt 1s orbital.

Q.31. A sub-shell with n = 6 , l = 2 can accommodate a maximum of
(a) 12 electrons
(b) 36 electrons
(c) 10 electrons
(d) 72 electrons

Answer

(c) 10 electrons
Explanation:
n = 6, ℓ = 2 means 6d → will have 5 orbitals.
Therefore max 10 electrons can be accommodated as each orbital can have maximum of 2 electrons.

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