Transition and InnerTransition Elements - Result Question 142
####42. The correct statement(s) about $Cr^{2+}$ and $Mn^{3+}$ is/are [atomic number of $Cr=24$ and $Mn=25$ ]
(2015 Adv.)
(a) $Cr^{2+}$ is a reducing agent
(b) $Mn^{3+}$ is an oxidising agent
(c) both $Cr^{2+}$ and $Mn^{3+}$ exhibit $d^{4}$ electronic configuration
(d) when $Cr^{2+}$ is used as a reducing agent, the chromium ion attains $d^{5}$ electronic configuration
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Answer:
Correct Answer: 42. $(a, b, c)$
Solution:
- In aqueous solution $Cr^{2+}\left(3 d^{4}\right)$ acts as a reducing agent, oxidising itself to $Cr^{3+}\left(3 d^{3}\right)$ that gives a completely half-field $t _{2 g}$ level in octahedral ligand field of $H _2 O$.
(b) $Mn^{3+}\left(3 d^{4}\right)$ is an oxidising agent as it is reduced to $Mn^{2+}\left(3 d^{5}\right)$, a completely half-filled stable configuration.
(c) Both $Cr^{2+}$ and $Mn^{3+}$ have $d^{4}$ configuration.
(d) $3 d^{4} Cr^{2+}(a q) \xrightarrow{\text { R.A }} Cr^{3+}(a q)+e^{-}$
Hence $(d)$ is wrong statement.
