Identify the compound which turns black with ammonia solution.

Nitrite $\left({\mathrm{NO}}_2^{-}\right)$ interferes in the ring-test of nitrate $\left({\mathrm{NO}}_3^{-}\right)$. Some following reagents can be used for the removal of nitrite:

I : Potassium dichromate (s)
II : $\mathrm{CO}{\left({\mathrm{NH}}_2\right)}_2$ (urea)
III : ${\mathrm{NH}}_2{\mathrm{SO}}_3\mathrm{H}$ (sulphamic acid)

IV: Zinc/sodium hydroxide

With respect to qualitative analysis of inorganic salt, how many of the following cations belong to group $IV?$

${\mathrm{Co}}^{2+},{\mathrm{Mg}}^{2+},{\mathrm{Ni}}^{2+},{\mathrm{Zn}}^{2+},{\mathrm{Sr}}^{2+},{\mathrm{Ca}}^{2+},{\mathrm{Mn}}^{2+},{\mathrm{Pb}}^{2+},{\mathrm{Al}}^{3+}$