Q66 / 180 · AIIMS 2018 (26 May) · Chemistry

Which is least stable in aqueous medium?

Correct answer
A
$\mathrm{Fe}^{2+}$
B
$\mathrm{Co}^{2+}$
C
$\mathrm{Ni}^{2+}$
D
$\mathrm{Mn}^{2+}$

Solution

$\mathrm{Fe}^{2+}\left(3 d^6\right)$ quickly oxidises to $\mathrm{Fe}^{3+}$ $\left(3 d^5\right.$, more stable) in aqueous medium.

Hence, the correct answer is option: 'A'.

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