NEET 2025 MCQ with Answer Explanation : “Quantum Mechanical Model”

Here below some basic MCQ’s about “Quantum Mechanical Model” with answer which is explained in details. Let’s check one by one which is given below.

MCQ 1
Which of the following statements about the quantum mechanical model of the atom is true?

A) Electrons move in fixed orbits around the nucleus.
B) The position and momentum of an electron can be known simultaneously with arbitrary precision.
C) Electrons exist in probabilistic orbitals, described by wave functions.
D) The energy of electrons is not quantized.

Answer: C) Electrons exist in probabilistic orbitals, described by wave functions.

Explanation: The quantum mechanical model introduces the concept of wave functions and probability distributions, meaning electrons do not have fixed orbits but exist in orbitals defined by probabilities. Options A and D are characteristic of the Bohr model, while B refers to the Heisenberg Uncertainty Principle, which states that position and momentum cannot both be precisely known at the same time.

MCQ 2
What does the principal quantum number (n) indicate in the quantum mechanical model of the atom?

A) Shape of the orbital
B) Orientation of the orbital
C) Size and energy of the orbital
D) Spin of the electron

Answer: C) Size and energy of the orbital.

Explanation: The principal quantum number (n) determines the energy level and size of an electron’s orbital. As n increases, the orbital’s energy and size increase. The shape of the orbital is indicated by the azimuthal quantum number (l), while orientation is specified by the magnetic quantum number (m_l), and spin is represented by the spin quantum number (m_s).

MCQ 3
The Schrödinger equation is fundamental to quantum mechanics because it:

A) Describes the motion of macroscopic objects.
B) Provides a way to calculate the energy levels of an electron in an atom.
C) Predicts the exact position of electrons.
D) Is used exclusively in chemical reactions.

Answer: B) Provides a way to calculate the energy levels of an electron in an atom.

Explanation: The Schrödinger equation is a key equation in quantum mechanics that describes how the quantum state of a physical system changes over time. It is used to calculate the allowed energy levels of electrons in atoms and to find the wave functions of particles. It does not predict exact positions (which is impossible due to the uncertainty principle) and is applicable in various areas of physics, not just chemical reactions.

MCQ 4
Which of the following correctly describes the concept of electron spin?

A) Electrons are stationary and do not spin.
B) Electron spin is a property that can take two values: +1/2 and -1/2.
C) Spin is related to the physical rotation of electrons around the nucleus.
D) Electrons spin in only one direction.

Answer: B) Electron spin is a property that can take two values: +1/2 and -1/2.

Explanation: Electron spin is a fundamental property of electrons, akin to angular momentum, and can be thought of as a form of intrinsic angular momentum. It does not refer to actual physical rotation but rather a quantum property. The values +1/2 and -1/2 represent the two possible spin states of an electron. Options A and C are incorrect, and option D is misleading since electrons can be in a superposition of spin states.

MCQ 5
What is the shape of an s orbital?

A) Dumbbell
B) Spherical
C) Double dumbbell
D) Linear

Answer: B) Spherical.

Explanation: An s orbital is spherical in shape, representing a region where there is a high probability of finding an electron. In contrast, p orbitals have a dumbbell shape, and d orbitals can be more complex.

MCQ 6
Which of the following quantum numbers describes the orientation of an orbital?

A) Principal quantum number (n)
B) Azimuthal quantum number (l)
C) Magnetic quantum number (m_l)
D) Spin quantum number (m_s)

Answer: C) Magnetic quantum number (m_l).

Explanation: The magnetic quantum number (m_l) specifies the orientation of an orbital in space. The principal quantum number (n) indicates the energy level, while the azimuthal quantum number (l) describes the shape, and the spin quantum number (m_s) refers to the electron’s spin.

MCQ 7
What does the Heisenberg Uncertainty Principle state?

A) Electrons move in definite paths.
B) The energy of an electron is always constant.
C) The position and momentum of a particle cannot both be precisely determined at the same time.
D) All particles have wave properties.

Answer: C) The position and momentum of a particle cannot both be precisely determined at the same time.

Explanation: The Heisenberg Uncertainty Principle highlights a fundamental limit to the precision with which pairs of physical properties, such as position and momentum, can be known simultaneously.

MCQ 8
Which of the following represents the maximum number of electrons that can occupy an orbital?

A) 1
B) 2
C) 6
D) 8

Answer: B) 2.

Explanation: Each orbital can hold a maximum of two electrons, and they must have opposite spins due to the Pauli Exclusion Principle.

MCQ 9
Which quantum number indicates the shape of an orbital?

A) Principal quantum number (n)
B) Azimuthal quantum number (l)
C) Magnetic quantum number (m_l)
D) Spin quantum number (m_s)

Answer: B) Azimuthal quantum number (l).

Explanation: The azimuthal quantum number (l) determines the shape of the orbital. For example, l = 0 corresponds to an s orbital, l = 1 to a p orbital, and l = 2 to a d orbital.

MCQ 10
What is the principle behind electron configurations in atoms?

A) Electrons fill orbitals in random order.
B) Electrons fill the lowest energy orbitals first (Aufbau principle).
C) All orbitals must be filled before any can be doubled up.
D) The total number of electrons in an atom is always equal to the atomic number.

Answer: B) Electrons fill the lowest energy orbitals first (Aufbau principle).

Explanation: The Aufbau principle states that electrons occupy the lowest energy orbitals available before moving to higher ones. This helps to determine the electron configuration of elements.