question_answer

With \[3{{d}^{4}}\] configuration, \[C{{r}^{2+}}\] acts as a reducing agent but \[M{{n}^{3+}}\] acts as an oxidising agent. Explain.

Answer:

                  \[C{{r}^{2+}}(3{{d}^{4}})\xrightarrow{\,}\,C{{r}^{3+}}(3{{d}^{3}})+{{e}^{-}};\]      \[M{{n}^{3+}}\,(3{{d}^{4}})+{{e}^{-}}\xrightarrow{{}}\,M{{n}^{2+}}(3{{d}^{5}})\] \[C{{r}^{2+}}\] acts as a reducing agent due to greater stability of \[C{{r}^{3+}}\] with exactly half-filled \[{{t}_{2g}}\] level. \[M{{n}^{3+}}\] acts as an oxidising agent due to extra stability of \[M{{n}^{2+}}\] ion with all half filled d-orbitals.