Engineering Questions with Answers - Multiple Choice Questions

Materials Science MCQ’s – Atomic Models

1 - Question

In the wave-mechanical model of an atom, degenerate energy levels have:
a) Equal energy
b) Equal number of electrons
c) Same shape
d) Electrons with the same spin
View Answer Answer: a
Explanation: Degenerate energy levels have equal energy. In an atom, the orbitals in the same subshell are degenerate in absence of an external magnetic field.

2 - Question

Paired electrons in an atom have equal values of all of the four quantum numbers.
a) True
b) False
View Answer Answer: b
Explanation: According to Pauli’s exclusion principle, no two electrons in an atom can have all four quantum numbers equal. Paired electrons have opposite spins.

3 - Question

Protons attract electrons. Then why do electrons not fall on the nucleus?
a) Neutrons repel the electrons
b) Electrons in ground state cannot radiate energy
c) At very small distances, protons repel electrons
d) Inner electrons repel those in outer orbitals
View Answer Answer: b
Explanation: In the ground state, electrons form standing waves. Standing waves are those in which energy is not transferred. Hence, electrons are bound to revolve around the nucleus with constant potential energy.

4 - Question

Number of atomic orbitals in nth shell is:
a) n2
b) 2n2
c) 2n + 1
d) n − 1
View Answer Answer: a
Explanation: Every shell contains n2 orbitals and every orbital can accommodate a maximum of 2 electrons. Hence a maximum of 2n2 electrons can reside in nth shell.

5 - Question

Electronic configuration of Cu is [Ar] 3d10 4s1. Which rule is violated in this configuration?
a) Aufbau Principle
b) Hund’s Rule of Maximum Multiplicity
c) Pauli’s Exclusion Principle
d) None of the mentioned
View Answer Answer: a
Explanation: According to the Aufbau principle, orbitals of lower energy are completely filled before electrons start occupying higher energy orbitals. But in copper, higher energy 3d is filled before lower energy 4s. Such violation of the Aufbau principle appears in about 20 elements.

6 - Question

When an electron shifts to an inner shell, it:
a) Absorbs photon
b) Emits a photon
c) Emits a positron
d) Absorbs a positron
View Answer Answer: b
Explanation: Generally, lower potential energy means more stability. Excited electrons lose energy in the form of photons to shift to stable empty inner shells. Positron is anti-particle of an electron.

7 - Question

Around 1911, Rutherford suggested a planetary model of atomic structure. Which of the following was not a proposition of this model?
a) Electrons revolve in circular orbits around the nucleus
b) Nucleus consists of protons and neutrons
c) Mass of atom is concentrated in the nucleus
d) Most of the volume in an atom is void
View Answer Answer: b
Explanation: Neutrons were not discovered by then. Rutherford only suggested that the nucleus has a positive charge, but did not comment on its structure.

8 - Question

Which of the Bohr’s postulates was incorrect?
a) Energy of electrons is quantized
b) Momentum of electrons is quantized
c) Electrons release energy when shifting from excited state to ground state
d) Electrons revolve around the nucleus in fixed circular orbits
View Answer Answer: d
Explanation: Heisenberg uncertainty principle implies that exact position and momentum of electrons cannot be known with certainty and hence, definite circular paths are not feasible. Certain regions around the nucleus (called orbitals) have a high probability of the existence of electrons

9 - Question

4f orbital has higher energy than 5p.
a) True
b) False
View Answer Answer: a
Explanation: Sum of principal and azimuthal quantum numbers for 4f is (4+3=) 7 and that for 5p is (5+1=) 6. As a general rule, higher the sum, higher is the energy.

10 - Question

Which of the following orbitals do not exist?
a) 3p
b) 4s
c) 2s
d) 3f
View Answer Answer: d
Explanation: For principal quantum number 3, only possible values of azimuthal quantum number are 0, 1, and 2. Azimuthal quantum number of an f-orbital is 3.

11 - Question

View Answer

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