JEE Main 2025 — Chemistry Inorganic Chemistry

2025mcqmedium

The metal ions that have the calculated spin only magnetic moment value of 4.9 B.M. are

A. $\mathrm{Cr}^{2+}$

B. $\mathrm{Fe}^{2+}$

C. $\mathrm{Fe}^{3+}$

D. $\mathrm{Co}^{2+}$

E. $\mathrm{Mn}^{3+}$

Choose the correct answer from the options given below

Official previous-year question

Held on 3 Apr 2025 · Verified 6 Jul 2026.

Options

A
A, C and E only
B
A, D and E only
C
B and E only
D
A, B and E only

Did you get this right?

Solution

Given magnetic moment $=4.9$ B.M.

We know M.M $=\sqrt{\mathrm{n}(\mathrm{n}+2)}$ B.M.

Where, $\mathrm{n} \rightarrow$ No. of unpaired $\mathrm{e}^{-}$

$4.9=\sqrt{\mathrm{n}(\mathrm{n}+2)}$

We get $\mathrm{n}=4$

(A) ${ }_{24} \mathrm{Cr}^{2+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^4$ (4 unpaired e)

(B) ${ }_{26} \mathrm{Fe}^{2+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^6$ (4 unpaired e)

(D) ${ }_{27} \mathrm{Co}^{2+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^7$ (3 unpaired $\mathrm{e}^{-}$ )

(E) ${ }_{25} \mathrm{Mn}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^4 \quad\left(4\right.$ unpaired $\left.\mathrm{e}^{-}\right)$

Your note

JEE Main Inorganic Chemistry in other years

Inorganic Chemistry 2026 Inorganic Chemistry 2024 Inorganic Chemistry 2023 Inorganic Chemistry 2022 Inorganic Chemistry 2021 Inorganic Chemistry 2020 Inorganic Chemistry 2019 Inorganic Chemistry 2018 Inorganic Chemistry 2017 Inorganic Chemistry 2016 Inorganic Chemistry 2015 Inorganic Chemistry 2014

Keep practicing Inorganic Chemistry

Work through every JEE Main Inorganic Chemistry PYQ, year by year.

Browse all Chemistry topics

Solution

Given magnetic moment $=4.9$ B.M.

We know M.M $=\sqrt{\mathrm{n}(\mathrm{n}+2)}$ B.M.

Where, $\mathrm{n} \rightarrow$ No. of unpaired $\mathrm{e}^{-}$

$4.9=\sqrt{\mathrm{n}(\mathrm{n}+2)}$

We get $\mathrm{n}=4$

(A) ${ }_{24} \mathrm{Cr}^{2+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^4$ (4 unpaired e)

(B) ${ }_{26} \mathrm{Fe}^{2+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^6$ (4 unpaired e)

(D) ${ }_{27} \mathrm{Co}^{2+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^7$ (3 unpaired $\mathrm{e}^{-}$ )

(E) ${ }_{25} \mathrm{Mn}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^4 \quad\left(4\right.$ unpaired $\left.\mathrm{e}^{-}\right)$

JEE Main 2025 — Chemistry Inorganic Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Inorganic Chemistry in other years

More JEE Main Inorganic Chemistry questions

Other Chemistry topics for JEE Main

Physical Chemistry

Organic Chemistry

Keep practicing Inorganic Chemistry

JEE Main 2025 — Chemistry Inorganic Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Inorganic Chemistry in other years

More JEE Main Inorganic Chemistry questions

Other Chemistry topics for JEE Main

Physical Chemistry

Organic Chemistry

Keep practicing Inorganic Chemistry