Electronic Configuration

Electronic Configuration MDCAT MCQs with answers

30 past paper MCQs on Electronic Configuration, 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.

Read the notes first Practise the unit as a quiz

1.Which of the following orbitals will be filled before $4p$? (MDCAT 2020)

  1. $4s$
  2. $2p$
  3. $3d$
  4. $5s$
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Correct answer: (c) $3d$

By the $(n+l)$ rule the order runs $4s$, $3d$, $4p$, so $3d$ fills first of these.

2.Which element has the ground state electronic configuration $1s^2\,2s^2\,2p^6\,3s^2\,3p^6$? (MDCAT 2022)

  1. Ar
  2. O
  3. Na
  4. S
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Correct answer: (a) Ar

Eighteen electrons filling up to $3p$ is argon.

3.When the $6d$ orbital is filled, the entering electron goes into: (MDCAT 2023)

  1. $7s$
  2. $7p$
  3. $8s$
  4. $5f$
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Correct answer: (b) $7p$

By the $(n+l)$ rule the next lowest set after $6d$ is $7p$.

4.Which element has the ground state electronic configuration $1s^2\,2s^2\,2p^6\,3s^2\,3p^6$? (MDCAT 2023)

  1. Cl
  2. K
  3. Ne
  4. Ar
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Correct answer: (d) Ar

Eighteen electrons in a closed shell arrangement is argon.

5.What is the proton number of the element that has four unpaired electrons in its ground state? (MDCAT 2023)

  1. 24
  2. 25
  3. 22
  4. 26
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Correct answer: (d) 26

Iron, $[\mathrm{Ar}]3d^64s^2$, has four unpaired $3d$ electrons.

6.Which of the following electronic configurations is correct for carbon? (MDCAT 2024)

  1. $1s^22s^22p^2$
  2. $1s^22s^22p^4$
  3. $1s^22s^22p^3$
  4. $1s^22s^22p^1$
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Correct answer: (a) $1s^22s^22p^2$

Carbon has six electrons, which fill $1s$ and $2s$ and leave two in $2p$.

7.Number of unpaired electrons present in the ground state of Fe3+ are (Atomic number of Fe=26). (UHS MDCAT 2025)

  1. Three
  2. Four
  3. Five
  4. Six
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Correct answer: (c) Five

Iron(III) is $[\mathrm{Ar}]3d^5$, and five d electrons stay unpaired.

8.Number of unpaired electrons In Boron in ground state is/are: (UHS MDCAT 2025)

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

Boron is $1s^2 2s^2 2p^1$, so the single p electron is the only unpaired one.

9.When 5d orbital is complete, the entering electron goes into: (NUMS MDCAT 2025)

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

By the $n+l$ rule the 6p subshell is filled after the 5d.

10.Which of the following is expected to be the most paramagnetic? (SIBA MDCAT 2025)

  1. H
  2. Be
  3. B
  4. C
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Correct answer: (d) C

Carbon is $1s^2 2s^2 2p^2$, with two unpaired p electrons, more than any of the others here.

11.Which of the following electronic configuration is correct for carbon? (UHS MDCAT 2024)

  1. 1s22s2p3
  2. 1s22s2p4
  3. 1s22s2p2
  4. 1s22s2p1
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Correct answer: (c) 1s22s2p2

Carbon has six electrons, $1s^2 2s^2 2p^2$.

12.Which element has the electronic configuration of noble-gas notation [Kr], 5s2, 4d? (KMU MDCAT 2024)

  1. Mo
  2. Se
  3. Sr
  4. Zr
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Correct answer: (d) Zr

Zirconium is $[\mathrm{Kr}]5s^2 4d^2$.

13.The element having the electronic configuration (Kr) 5s24d8 is: (NUMS MDCAT 2024)

  1. Sr
  2. Ru
  3. Pd
  4. Zr
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Correct answer: (c) Pd

Filling to $[\mathrm{Kr}]5s^2 4d^8$ accounts for 46 electrons, which is palladium.

14.Which element has the ground state electronic configuration of 1s2, 2s2, 2p6, 3s2, 3p6? (UHS MDCAT 2023)

  1. Ar
  2. Cl
  3. Na
  4. S
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Correct answer: (a) Ar

Eighteen electrons filled to $3p^6$ is argon.

15.What is the proton (atomic number) of an element that has four unpaired electrons in its ground state? (UHS MDCAT 2023)

  1. 6
  2. 14
  3. 22
  4. 26
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Correct answer: (d) 26

Iron, $[\mathrm{Ar}]3d^6 4s^2$, has four unpaired d electrons.

16.The electronic configuration for degenerated orbitals is explained by: (SZABMU MDCAT 2023)

  1. Aufbau Principle
  2. 𝑛 + 𝑙 rule
  3. Hund’s rule
  4. Pauli exclusion principle
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Correct answer: (c) Hund’s rule

Hund’s rule fills degenerate orbitals singly before any is doubled.

17.The electronic configuration for degenerate orbitals is explained by: (NUMS MDCAT 2023)

  1. Aufbau Principle
  2. n + l rule
  3. Hund's rule
  4. Pauli exclusion principle
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Correct answer: (c) Hund's rule

Hund’s rule fills degenerate orbitals singly before any is doubled.

18.When 6d orbital is filled, the entering electron goes into? (UHS MDCAT 2023)

  1. 7f
  2. 7d
  3. 7p
  4. 7s
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Correct answer: (c) 7p

By the $n+l$ rule the 7p subshell follows the 6d.

19.How many unpaired electrons are there in the Nitrogen atom? (PMC MDCAT 2022)

  1. 3
  2. 4
  3. 5
  4. 6
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Correct answer: (a) 3

Nitrogen is $1s^2 2s^2 2p^3$, and by Hund’s rule the three p electrons stay unpaired.

20.The valence shell electronic configuration of Ca is Ar[ ]: (PMC MDCAT 2022)

  1. 1s2
  2. 2s2
  3. 3s2
  4. 4s2
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Correct answer: (d) 4s2

Calcium is $[\mathrm{Ar}]4s^2$.

21.Which of the following atomic orbital has lowest energy? (PMC MDCAT 2022)

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

The 1s orbital is nearest the nucleus and lowest in energy.

22.Atomic numbers of chromium (Cr) is 24. Correct electronic configuration of Cr is: (PMC MDCAT 2022)

  1. [Ar]3d54s1
  2. [Ar]3d54s2
  3. [Ar]3d04s0
  4. [Ar]3d44s2
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Correct answer: (a) [Ar]3d54s1

A half filled d subshell is stable, so chromium is $[\mathrm{Ar}]3d^5 4s^1$.

23.How many electrons does calcium have in the 3p orbital? (PMC MDCAT 2022)

  1. 5
  2. 6
  3. 2
  4. 3
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Correct answer: (b) 6

Calcium is $[\mathrm{Ne}]3s^2 3p^6 4s^2$, so its 3p subshell is full with six.

24.The atomic number of calcium is 20. The electronic structure of a calcium ion can be represented as: (PMC MDCAT 2022)

  1. 2,8
  2. 2,8,4
  3. 2,8,8
  4. 2,8,8,2
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Correct answer: (c) 2,8,8

The calcium ion has lost its two 4s electrons, leaving the argon structure 2,8,8.

25.Apply n+l rule and calculate which of the following orbital has maximum energy? (NUMS MDCAT 2022)

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

The 4s orbital has the largest $n+l$ of these, so it lies highest.

26.Sodium-11 has the electronic configuration: (PMC Practice 2021)

  1. [He] 2s1
  2. [Ne] 3s1
  3. [Ne] 3s2
  4. [He] 2s2
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Correct answer: (b) [Ne] 3s1

Sodium is $[\mathrm{Ne}]3s^1$.

27.Which pair has 1 electron in it’s ‘s’ orbital? (PMC MDCAT 2020)

  1. Li & Fe
  2. Na & Cr
  3. K & Mn
  4. H & He
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Correct answer: (b) Na & Cr

Sodium is $3s^1$ and chromium $4s^1$, each with a single s electron in its outer shell.

28.Which of the following is the electronic configuration of Cr? (UHS MDCAT 2019)

  1. [Ar] 3d5 4s2
  2. [Ar] 3d5 4s1
  3. [Ar] 3d4 4s2
  4. [Ar] 3d6 4s0
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Correct answer: (b) [Ar] 3d5 4s1

A half filled d subshell is stable, so chromium is $[\mathrm{Ar}]3d^5 4s^1$.

29.Which is the correct electronic configuration of Chromium (24Cr)? (UHS MDCAT 2018)

  1. 1s2, 2s2, 3s2, 2p6, 3p6, 4s2, 3d6
  2. 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d4
  3. 1s1, 2s2, 2p6, 3s2, 3p6, 3d6
  4. 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
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Correct answer: (d) 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5

A half filled d subshell is stable, so chromium is $[\mathrm{Ar}]4s^1 3d^5$.

30.Which element of 3d series of periodic table shows the electronic configuration of 3d8, 4s2? (UHS MDCAT 2016)

  1. Copper
  2. Cobalt
  3. Zinc
  4. Ni
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Correct answer: (d) Ni

$[\mathrm{Ar}]3d^8 4s^2$ accounts for 28 electrons, which is nickel.

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