Free Electronic Configuration MCQs with Answers
103 Electronic Configuration MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Electronic configuration describes how electrons occupy shells, subshells and orbitals around an atom. Questions use the Aufbau principle, Pauli exclusion principle and Hund's rule to write configurations, identify valence electrons, form ions and explain periodic trends, including common exceptions such as chromium and copper.
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- A. pair up in the first orbital before entering the next
- B. occupy separate orbitals with parallel spins before pairing
- C. occupy the orbital of highest energy first
- D. always pair with opposite spins immediately
Explanation: Electrons repel one another, so they spread across orbitals of equal energy singly and with parallel spins before any orbital takes a…
Correct answer: occupy separate orbitals with parallel spins before pairing- A. [Ar] 3d4 4s2
- B. [Ar] 3d5 4s1
- C. [Ar] 3d6 4s0
- D. [Ar] 3d3 4s3
Explanation: Chromium promotes one 4s electron into the 3d subshell because a half filled d5 configuration alongside a half filled 4s is more stable…
Correct answer: [Ar] 3d5 4s1- A. 4p
- B. 3d
- C. 4d
- D. 5s
Explanation: Orbitals fill in order of increasing n plus l, and where that sum ties the lower n goes first.
Correct answer: 3d- A. pair up in the lowest orbital first
- B. occupy separate orbitals singly with parallel spins before any pairing occurs
- C. always have opposite spins
- D. fill the highest energy orbital first
Explanation: Spreading out into empty orbitals minimises electron electron repulsion, so nitrogen's three 2p electrons occupy the three separate p…
Correct answer: occupy separate orbitals singly with parallel spins before any pairing occurs- A. no two electrons in an atom can have the same set of all four quantum numbers
- B. electrons always pair up
- C. orbitals fill in order of increasing energy
- D. electrons occupy the nucleus
Explanation: Because the first three quantum numbers define an orbital, the principle limits any orbital to two electrons, which must then differ in…
Correct answer: no two electrons in an atom can have the same set of all four quantum numbers- A. 3d
- B. 4s
- C. 4p
- D. 4d
Explanation: For 4s the sum is 4 plus 0, that is 4, while for 3d it is 3 plus 2, that is 5, so the lower sum fills first and 4s is occupied before 3d.
Correct answer: 4s- A. 1s2 2s2 2p6 3s2 3p5
- B. 1s2 2s2 2p6 3s2 3p6
- C. 1s2 2s2 2p6 3s2 3p4
- D. 1s2 2s2 2p6 3s1
Explanation: Chlorine gains one electron to form the chloride ion, taking its total to 18 and giving it the argon configuration with a complete octet.
Correct answer: 1s2 2s2 2p6 3s2 3p6- A. their nuclei are unstable
- B. a half filled or completely filled d subshell is more stable
- C. they lose electrons easily
- D. the 4s orbital does not exist for them
Explanation: Promoting one 4s electron gives chromium a 3d5 4s1 arrangement and copper a 3d10 4s1 arrangement, both of which gain stability from the…
Correct answer: a half filled or completely filled d subshell is more stable- A. electron affinity
- B. ionisation energy
- C. electronegativity
- D. lattice energy
Explanation: Ionisation energy is always endothermic because work must be done against the nuclear attraction, and it rises steeply for each successive…
Correct answer: ionisation energy10. Number of unpaired electrons present in the ground state of Fe3+ are (Atomic number of Fe = 26).
- A. Three
- B. Four
- C. Five
- D. Six
Explanation: Neutral iron is [Ar] 3d6 4s2, and forming Fe3+ removes both 4s electrons and one 3d electron, leaving 3d5.
Correct answer: Five- A. 1
- B. 2
- C. 3
- D. 4
Explanation: Boron has atomic number 5, so its configuration is 1s2 2s2 2p1 and the single 2p electron is the only unpaired one.
Correct answer: 1- A. H
- B. He+¹
- C. Li+²
- D. Be+³
Explanation: For a hydrogen-like species in the first shell, electron energy is E = -13.6 Z^2/1^2 eV, so it becomes more negative as nuclear charge Z…
Correct answer: Be+³13. Atomic number of Mn is 25 what is the electronic configuration in the ground state________________?
- A. 1s2 2s2 2p6 3s2 3p6 3d7
- B. 1s2 2s2 2p6 3s2 3p6 4s2 4p5
- C. 1s2 2s2 2p6 3s2 3p5 3d10
- D. 1s2 2s2 2p6 3s2 3p6 4s23d5
Explanation: Manganese has atomic number 25, so a neutral atom contains 25 electrons.
Correct answer: 1s2 2s2 2p6 3s2 3p6 4s23d5- A. isotope
- B. isobar
- C. isotone
- D. None of these
Explanation: Atoms of different elements having the same number of neutrons are called isotones.
Correct answer: isotone- A. 1s2,2s2,2p6
- B. 1s2,2s2,2p6,3s2
- C. 1s2,2s2,2p6,3s1
- D. None of these
Explanation: Sodium has atomic number 11, so its 11 electrons fill as 1s2, 2s2, 2p6 and then 3s1.
Correct answer: 1s2,2s2,2p6,3s1- A. Ne, 4p2
- B. Ar, 4s2
- C. Ne, 4s2
- D. Kr,4p2
Explanation: Calcium has atomic number 20, and the preceding noble gas is argon, atomic number 18; its remaining two electrons occupy 4s, giving [Ar]…
Correct answer: Ar, 4s2- A. Carbon=0, Oxygen=0
- B. Carbon= +1, Oxygen= -1
- C. Carbon= -1, Oxygen= +1
- D. Carbon=0, Oxygen= -1
Explanation: The major Lewis structure of CO has a triple bond and one lone pair on each atom; formal charge is calculated as valence electrons minus…
Correct answer: Carbon= -1, Oxygen= +1- A. p-electrons in Ne(Z = 10)
- B. s-electrons in Mg(Z = 12)
- C. d-electrons in Fe(Z = 26)
- D. p-electrons in CI(Z = 17)
Explanation: Fe has the configuration [Ar] 3d6 4s2, so Fe2+ loses the 4s electrons and has six 3d electrons.
Correct answer: p-electrons in CI(Z = 17)- A. Nucleon numbera
- B. Mass number
- C. Atomic number
- D. Both A and B
Explanation: The sum of protons and neutrons is called the mass number, and it is also called the nucleon number because protons and neutrons are…
Correct answer: Both A and B- A. 1s2 2s2 2p3
- B. 1s2 2s2 2p6 3s2 3p1
- C. 1s2 2s2 2p4
- D. 1s2 2s2 2p6 3s2 3p6 4s2 3d1
Explanation: Group IIIA, now called Group 13, elements have two electrons in the outer s subshell and one in the outer p subshell, giving the valence…
Correct answer: 1s2 2s2 2p6 3s2 3p1Electronic Configuration MCQs: common questions
Are these Electronic Configuration MCQs free?
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There are 103 Electronic Configuration MCQs in the Chemistry bank, shown 20 to a page with the correct answer and an explanation on each.
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