Which of the following will not act as an oxidising agent?

How would you account for the following:
$(i)$ Of the $d^{4}$ species,$Cr^{2+}$ is strongly reducing while $Mn^{3+}$ is strongly oxidising.
$(ii)$ $Co^{2+}$ is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.
$(iii)$ The $d^{1}$ configuration is very unstable in ions.

Concentrated sodium hydroxide can separate a mixture of

Which of the following compounds reacts with $NaOH$ and $Na_2O_2$ to produce a yellow color?

$Cu^{2+}$ ions will be reduced to $Cu^{+}$ ions by the addition of an aqueous solution of

Transition elements with lower oxidation states act as........