Question

Which of the following statements is false?

• A. Because of the $d^{4}$ species, manganese $\left(\right.III\left.\right)$ is
  strongly reducing, while $Cr^{2 +}$ is strongly oxidising.
• B. Cobalt $\left(\right.II\left.\right)$ 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) $Cr^{2 +}$ is reducing as it involves change from $d^{4}$ to $d^{3}$ , the latter is more stable configuration $\left(t_{29}^{3}\right)Mn\left(\right.lll\left.\right)$ to $Mn\left(\right.ll\left.\right)$ 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 $d^{1}.$