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

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