Which of the following is the use of potassium permanganate $(KMnO_4)$?

Copper sulphate is not used:

Silver halides are used in photography because:

The number of terminal oxygen atoms present in the product $B$ obtained from the following reaction is $....$
$4FeCr_2O_4 + 8Na_2CO_3 + 7O_2 \rightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8CO_2$
$2Na_2CrO_4 + 2H^{+} \rightarrow B + H_2O + 2Na^{+}$

The oxidation number of $Mn$ in the product of alkaline oxidative fusion of $MnO_2$ is

Give the formulas of the oxocations of the $3d$ series metals.