The chemical formula of nitrogen dioxide is ${\mathrm{NO}}_2$. Thus, to liberate nitrogen dioxide, a salt must have at least one nitrogen atom.

Now, as salt $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$ has two nitrogen atoms, thus it can release nitrogen dioxide gas. Lead(II) nitrate crystals decompose and break down into lead(II) oxide, oxygen, and nitrogen dioxide when heated. 

$2\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{s}\right)\stackrel{\mathrm{Heat}}{\to }2\mathrm{PbO}\left(\mathrm{s}\right)+4{\mathrm{NO}}_2 \left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$

Lead nitrate occasionally appears in pyrotechnics like fireworks due to its characteristics.

The hydrated salts$({\mathrm{ZnSO}}_4.7{\mathrm{H}}_2\mathrm{O}, {\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O})$ lose their water of crystallization to produce anhydrous salts.

Hence, the correct option is (A).