Question

Which of the following statements is false?

• A. Because of the $d^4$ species, manganese $(III)$ is
  strongly reducing, while $C{r}^{2+}$ is strongly oxidising.
• B. Cobalt $(II)$ is stable in aqueous solution, but
  in the presence of complexing reagents, it
  is easily oxidized.
• C. The $d^1$ configuration is very unstable in ions.
• D. None of these

Answer 1

Answer: (A)

(1) $C{r}^{2+}$ is reducing as it involves change from $d^4$ to $d^3$ , the latter is more stable configuration $\left(t_{29}^3\right)Mn(lll)$ to $Mn(ll)$ is from $3d^4$ to $3d^5$ again $3d^5$ is an extra stable configuration.
(2) Due to higher CFSE of $d^6$ configuration in presence of ligands which more than compensates the $3rd$ IE.
(3) The hydration or lattice energy more than compensates the ionisation enthalpy involved in removing electron from $d^1.$