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NEET Chemistry: Quantum mechanics Practice Questions

14 free multiple-choice questions on Quantum mechanics (Atomic Structure) for NEET Chemistry, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. If a system has a set of discrete energy values, it means the system can only occupy those specific energy states. This restriction is described by which quantum mechanical postulate?

    • AThe Pauli Exclusion Principle
    • BQuantization of energy levels
    • CSpin-orbit coupling
    • DThe Correspondence Principle
    Show answer & explanation

    Correct answer: B — Quantization of energy levels

    The restriction to specific, measurable energy values is the definition of energy quantization.

  2. Q2. Which of the following quantum numbers is used to describe the shape of an orbital?

    • Al
    • Bm_s
    • Cm_l
    • Dn
    Show answer & explanation

    Correct answer: A — l

    The azimuthal quantum number, 'l' (angular momentum quantum number), determines the shape of the orbital (s, p, d, f).

  3. Q3. In the context of the Bohr model/quantum mechanics, what does the principal quantum number (n) primarily define?

    • AThe orientation of the orbital
    • BThe spin of the electron
    • CThe size and energy level of the orbital
    • DThe total energy of the electron
    Show answer & explanation

    Correct answer: C — The size and energy level of the orbital

    The principal quantum number n defines the main energy level or shell, which dictates the size and energy of the orbital.

  4. Q4. In the context of the Bohr model, energy levels are discrete. What does this imply about the electron's motion around the nucleus?

    • AThe electron moves randomly
    • BThe electron can possess any kinetic energy
    • CThe electron can only exist in specific, fixed orbits
    • DThe electron interacts continuously with the nucleus
    Show answer & explanation

    Correct answer: C — The electron can only exist in specific, fixed orbits

    The discreteness of energy levels implies that the electron can only exist in specific, well-defined stationary orbits with fixed, quantized energies.

  5. Q5. The angular momentum of an electron is quantized. This means that the possible values for angular momentum are restricted to:

    • AContinuous values
    • BHalf-integer values
    • CAny real number
    • DInteger multiples of h/2π
    Show answer & explanation

    Correct answer: D — Integer multiples of h/2π

    Due to the quantization rules of angular momentum, the values are restricted to integer multiples of ħ (or h/2π), leading to discrete, specific values.

  6. Q6. Which quantum number determines the size of the electron's orbital?

    • AAzimuthal quantum number (l)
    • BMagnetic quantum number (m_l)
    • CSpin quantum number (m_s)
    • DPrincipal quantum number (n)
    Show answer & explanation

    Correct answer: D — Principal quantum number (n)

    The principal quantum number (n) determines the principal energy level and thus the overall size of the electron orbital.

  7. Q7. The maximum number of orbitals that can be present in a subshell with azimuthal quantum number l=2 is:

    • A9
    • B3
    • C5
    • D7
    Show answer & explanation

    Correct answer: C — 5

    For a given l, the magnetic quantum number m_l can take values from -l to +l. For l=2 (d-subshell), m_l values are -2, -1, 0, 1, 2, resulting in 5 orbitals.

  8. Q8. The energy of an electron in an orbit is quantized. Which equation is fundamental to describing the energy levels in a hydrogen atom according to quantum mechanics?

    • ASchrödinger wave equation
    • BDe Broglie relation
    • CPauli Exclusion Principle
    • DHeisenberg Uncertainty Principle
    Show answer & explanation

    Correct answer: A — Schrödinger wave equation

    The time-independent Schrödinger wave equation is the fundamental equation used to determine the allowed energy states and wave functions for electrons in an atom.

  9. Q9. Which quantum number specifies the orientation of an orbital in space?

    • APrincipal quantum number
    • BSpin quantum number
    • CMagnetic quantum number
    • DAzimuthal quantum number
    Show answer & explanation

    Correct answer: C — Magnetic quantum number

    The magnetic quantum number (mₗ) specifies the orientation of the orbital in three-dimensional space, determining the specific orbital within a subshell.

  10. Q10. The existence of discrete energy levels in an atom is fundamentally related to the concept of:

    • AWave-particle duality
    • BClassical mechanics
    • CRelativistic effects
    • DQuantization
    Show answer & explanation

    Correct answer: D — Quantization

    The fact that energy exists in discrete steps rather than continuously is the essence of energy quantization, which is a core concept derived from quantum mechanics.

  11. Q11. The relationship between the principal quantum number (n) and the number of radial nodes in an orbital is given by:

    • An-1
    • Bn
    • C2n-1
    • Dn²-1
    Show answer & explanation

    Correct answer: D — n²-1

    The number of radial nodes in an orbital is given by the formula n-1. For n=1 (1s), nodes = 0. For n=2 (2s, 2p), nodes = 1.

  12. Q12. Which quantum number determines the principal energy level of an electron in an atom?

    • AMagnetic quantum number
    • BSpin quantum number
    • CPrincipal quantum number
    • DAzimuthal quantum number
    Show answer & explanation

    Correct answer: C — Principal quantum number

    The principal quantum number (n) defines the main energy level or shell of an electron, determining the size and energy of the orbital.

  13. Q13. Which of the following quantum numbers determines the shape of an atomic orbital?

    • AAzimuthal (or angular momentum) quantum number (l)
    • BSpin quantum number (m_s)
    • CPrincipal quantum number (n)
    • DMagnetic quantum number (m_l)
    Show answer & explanation

    Correct answer: A — Azimuthal (or angular momentum) quantum number (l)

    The azimuthal quantum number (l) determines the shape of the orbital (s, p, d, f). The principal quantum number (n) determines the energy level, and the magnetic quantum number (m_l) determines the orientation of the orbital in space.

  14. Q14. Which principle states that no two electrons in an atom can have the exact same set of four quantum numbers?

    • AHeisenberg Uncertainty Principle
    • BAufbau Principle
    • CPauli Exclusion Principle
    • DHund's Rule
    Show answer & explanation

    Correct answer: C — Pauli Exclusion Principle

    The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of quantum numbers, which is fundamental to atomic structure.

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