The nitrate which on thermal decomposition leaves behind a residue which is yellow when hot and white when cold:

1. Lead nitrate
2. Ammonium nitrate
3. Copper nitrate.
4. Zinc nitrate

Zinc nitrate

Reason —

$\begin{matrix} 2\text{Zn(NO}$3)2 &\longrightarrow & \text{2ZnO} & + & 4\text{NO}2 &+ & \text{O}2 \ \text{[Zinc} & & \text{[Zinc nitrate - white]} & & \text{[Carbon} \ \text{carbonate]} & & \text{[yellow - hot]} & & \text{dioxide]} \ \text{[white]} & & \text{[white - cold]} \end{matrix}

Zinc nitrate decomposes to produces zinc oxide, which is yellow when hot and white when cold