Arrange the following divalent ions in decreasing order of their spin only magnetic moment:
(A) Ti2+
(B) Zn2+
(C) Mn2+
(D) Fe2+
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (C), (D), (A), (B)
A magnetic moment comes from unpaired electrons, and the spin-only moment is μ = √n(n+2) BM, so the order follows n. For each ion, the 4s electrons are removed first:
Ti (Z = 22), [Ar]3d24s2 → \( \ce{Ti^{2+}} \): 3d2, n = 2
Zn (Z = 30), [Ar]3d104s2 → \( \ce{Zn^{2+}} \): 3d10, n = 0
Mn (Z = 25), [Ar]3d54s2 → \( \ce{Mn^{2+}} \): 3d5, n = 5
Fe (Z = 26), [Ar]3d64s2 → \( \ce{Fe^{2+}} \): 3d6, n = 4
\( \displaystyle \mathrm{Mn^{2+}}:\ \sqrt{5\times7}=5.92\ \mathrm{BM} \)
\( \displaystyle \mathrm{Fe^{2+}}:\ \sqrt{4\times6}=4.90\ \mathrm{BM} \)
\( \displaystyle \mathrm{Ti^{2+}}:\ \sqrt{2\times4}=2.83\ \mathrm{BM} \)
\( \displaystyle \mathrm{Zn^{2+}}:\ 0 \)
Shortcut: The moment rises with the number of unpaired electrons, so there is no need to calculate √n(n+2). Just compare 5, 4, 2 and 0.
NCERT (2026-27 edition):
Magnetic Properties – …
