JEE Main · 2021 · Shift-IeasyDNF-023

In which of the following pairs, the outermost electronic configuration will be the same?

d & f-Block Elements · Class 12 · JEE Main Previous Year Question

Question

In which of the following pairs, the outermost electronic configuration will be the same?

Options

a
$\text{Cr}^+$ and $\text{Mn}^{2+}$
✓
b
$\text{Ni}^{2+}$ and $\text{Cu}^+$
c
$\text{Fe}^{2+}$ and $\text{Co}^+$
d
$\text{V}^{2+}$ and $\text{Cr}^+$

Correct Answera

$\text{Cr}^+$ and $\text{Mn}^{2+}$

Detailed Solution

Finding outermost (3d + 4s) configurations:

Option (1):

Cr (Z=24): $[\text{Ar}]\, 3d^5\, 4s^1$ → $\text{Cr}^+$ : removes 4s¹ → $3d^5$ ✓
Mn (Z=25): $[\text{Ar}]\, 3d^5\, 4s^2$ → $\text{Mn}^{2+}$ : removes 4s² → $3d^5$ ✓

Both have $3d^5$ outermost configuration. ✓

Checking others:

$\text{Ni}^{2+}$ : $3d^8$ ; $\text{Cu}^+$ : $3d^{10}$ ✗
$\text{Fe}^{2+}$ : $3d^6$ ; $\text{Co}^+$ : $3d^7 4s^1$ ✗
$\text{V}^{2+}$ : $3d^3$ ; $\text{Cr}^+$ : $3d^5$ ✗

Answer: Option (1) — $\text{Cr}^+$ and $\text{Mn}^{2+}$

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