JEE Main · 2021 · Shift-IIeasyDNF-016

Identify the element for which electronic configuration in +3 oxidation state is [Ar]\, 3d5:

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

Question

Identify the element for which electronic configuration in +3 oxidation state is $[\text{Ar}]\, 3d^5$ :

Options

a
Ru
b
Mn
c
Co
d
Fe
✓

Correct Answerd

Detailed Solution

Need M³⁺ = $[\text{Ar}]\, 3d^5$

M³⁺ is formed by removing 2 electrons from 4s and 1 from 3d. So neutral atom = $[\text{Ar}]\, 3d^6\, 4s^2$ .

| Element | Z | Ground Config | M³⁺ Config | |---------|---|---------------|------------| | Ru | 44 | [Kr] $4d^7 5s^1$ | $4d^5$ (not [Ar] core) | | Mn | 25 | [Ar] $3d^5 4s^2$ | $3d^4$ ✗ | | Co | 27 | [Ar] $3d^7 4s^2$ | $3d^6$ ✗ | | Fe | 26 | [Ar] $3d^6 4s^2$ | $3d^5$ ✓ |

$\text{Fe}^{3+}$ : $[\text{Ar}]\, 3d^5$ — half-filled, extra stable.

Answer: Option (4) — Fe

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