Quantum Numbers and Orbitals

Quantum Numbers and Orbitals MDCAT MCQs with answers

26 past paper MCQs on Quantum Numbers and Orbitals, from the Atomic Structure unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.The maximum number of electrons that can be placed in one orbital is: (MDCAT 2020)

  1. 1
  2. 2
  3. 3
  4. 4
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Correct answer: (b) 2

The Pauli exclusion principle allows two electrons of opposite spin in one orbital.

2.According to which scientist is the probability of finding an electron at a certain position possible? (MDCAT 2022)

  1. Bohr
  2. de Broglie
  3. Hund
  4. Schrodinger
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Correct answer: (d) Schrodinger

The square of the wave function of the Schrodinger equation gives the probability of finding the electron in a region, which is what an orbital is.

3.Which set of quantum numbers is not allowed for an electron. (UHS MDCAT 2025)

  1. n=2, l=1, m=0, s=+1/2
  2. n=3, l=0, m=0, s=-1/2
  3. n=2, l=2, m=+1, s=+1/2
  4. n=1, l=0, m=0, s=+1/2
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Correct answer: (c) n=2, l=2, m=+1, s=+1/2

The azimuthal quantum number cannot reach the principal one, so $l=2$ is impossible when $n=2$.

4.Shape of orbital is determined by quantum number: (UHS MDCAT 2025)

  1. n
  2. l
  3. m
  4. s
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Correct answer: (b) l

The azimuthal quantum number $l$ fixes the shape of the orbital; $n$ fixes its size.

5.The number of electrons in a subshell can be calculated by the formula: (NUMS MDCAT 2025)

  1. 2l + 1
  2. 2l + 2
  3. 2(2 + l)
  4. 2(2l + 1)
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Correct answer: (d) 2(2l + 1)

A subshell holds $2(2l+1)$ electrons, so two in s, six in p and ten in d.

6.Number of electron with l=2 in an atom having atomic number 23 is: (SZABMU MDCAT 2025)

  1. 2
  2. 3
  3. 4
  4. 5
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Correct answer: (b) 3

Vanadium is $[\mathrm{Ar}]3d^3 4s^2$, and $l=2$ means the d subshell, which holds three electrons.

7.Which of the following sub-shell does not exist? (KMU MDCAT 2024)

  1. 1p
  2. 1s
  3. 5d
  4. 6f
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Correct answer: (a) 1p

The first shell has $l=0$ only, so there is no 1p subshell.

8.The value of 'l' for 4p orbital is: (NUMS MDCAT 2024)

  1. 0
  2. 1
  3. 2
  4. 3
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Correct answer: (b) 1

A p orbital has $l=1$ whatever its shell.

9.Choose the correct quantum numbers: (NUMS MDCAT 2024)

  1. n=3, l=2, m=0, s=+1/2
  2. n=-3, l=3, m=0, s=-1/2
  3. n=4, l=3, m=4, s=+1/2
  4. n=4, l=2, m=4, s=-1/2
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Correct answer: (a) n=3, l=2, m=0, s=+1/2

Only the first set obeys the rules: $l$ below $n$, and $m$ within $\pm l$.

10.Principle quantum number is represented by the symbol: (SZABMU MDCAT 2023)

  1. m
  2. n
  3. s
  4. l
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Correct answer: (b) n

The principal quantum number is $n$.

11.Shape of the sub shell is explained by which quantum number: (SZABMU MDCAT 2023)

  1. Principal quantum number
  2. Azimuthal quantum number
  3. Magnetic quantum number
  4. Spin quantum number
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Correct answer: (b) Azimuthal quantum number

The azimuthal quantum number $l$ fixes the shape of the subshell.

12.Maximum number of electrons which can be placed in one orbital is: (SZABMU MDCAT 2023)

  1. 1
  2. 2
  3. 3
  4. 4
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Correct answer: (b) 2

No two electrons may share all four quantum numbers, so an orbital holds two of opposite spin.

13.If value of azimuthal quantum number is 2 then total values of magnetic quantum number will be: (NUMS MDCAT 2023)

  1. 03
  2. 05
  3. 07
  4. 10
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Correct answer: (b) 05

With $l=2$ the magnetic quantum number runs from $-2$ to $+2$, five values in all.

14.Which of the following quantum number is not obtained from Schrodinger Wave equation? (NUMS MDCAT 2023)

  1. Principal Quantum Number
  2. Spin Quantum Number
  3. Azimuthal Quantum Number
  4. Magnetic Quantum Number
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Correct answer: (b) Spin Quantum Number

The wave equation gives $n$, $l$ and $m$; the spin quantum number was added to account for the doubling of lines.

15.Which of the following orbital is closer to the nucleus? (PMC MDCAT 2022)

  1. 3d
  2. 2p
  3. 3p
  4. 3s
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Correct answer: (b) 2p

The lower the principal quantum number the nearer the shell, and 2p is nearer than any of the third shell.

16.How many electrons are present in the orbital having n=1, l=0, m=0? (PMC MDCAT 2022)

  1. 3
  2. 2
  3. 4
  4. 5
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Correct answer: (b) 2

Those numbers name the 1s orbital, which holds two electrons of opposite spin.

17.Which subshells are present In M shell? (PMC MDCAT 2022)

  1. s
  2. s, p
  3. s, p, d
  4. s, p, d, f
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Correct answer: (c) s, p, d

The third shell has $l=0,1,2$, that is s, p and d.

18.The maximum number of electrons which can be accommodated in all orbital for which I=3 is: (PMC MDCAT 2022)

  1. 6
  2. 14
  3. 10
  4. 18
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Correct answer: (b) 14

With $l=3$ there are seven orbitals, holding fourteen electrons.

19.The value of Azimuthal quantum number (I) depends upon: (PMC MDCAT 2022)

  1. n
  2. m
  3. s
  4. p
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Correct answer: (a) n

For a given $n$ the azimuthal number runs from $0$ to $n-1$.

20.Maximum electrons that can be placed in p subshell are: (NUMS MDCAT 2022)

  1. 2
  2. 6
  3. 10
  4. 14
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Correct answer: (b) 6

A p subshell has three orbitals, holding six electrons.

21.The shape of an orbital is determined by which quantum number? (NUMS MDCAT 2022)

  1. n
  2. l
  3. m
  4. s
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Correct answer: (b) l

The azimuthal quantum number $l$ fixes the shape.

22.The shielding effect is also called? (PMC Practice 2021)

  1. Zee effect
  2. Screening effect
  3. Negative effect
  4. Reducing effect
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Correct answer: (b) Screening effect

The inner electrons screen the outer ones from the nucleus, which is why it is called screening.

23.The formula for calculating the number of electrons in subshells or sub-energy levels is: (PMC Practice 2021)

  1. 2l+1
  2. 2(l+1)
  3. 2(2l+1)
  4. 2(2l-1)
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Correct answer: (c) 2(2l+1)

A subshell holds $2(2l+1)$ electrons.

24.Quantum number values for ‘2p’ orbitals are: (PMC MDCAT 2020)

  1. n=2, l=1
  2. n=1, l=2
  3. n=1, l=0
  4. n=2, l=0
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Correct answer: (a) n=2, l=1

The 2p orbital has $n=2$ and $l=1$.

25.The relationship between quantum number n and l is: (PMC MDCAT 2020)

  1. n = l – 1
  2. l = n – 2
  3. l = n – 1
  4. n = l – 2
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Correct answer: (c) l = n – 1

For a given $n$, $l$ runs from zero up to $n-1$.

26.The maximum number of electrons in electronic configuration can be calculated by using formula: (UHS MDCAT 2016)

  1. 2(2l + 1)
  2. 2n2 + 2
  3. 2n2
  4. 2n2 + 1
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Correct answer: (c) 2n2

A shell holds $2n^2$ electrons.

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