A colorless water-soluble compound on strong heating liberates a brown coloured gas and leaves a yellow residue that turns white on cooling. An aqueous solution of the original solid gives a white precipitate with $$(\mathrm{NH_4})_2\mathrm S$$. The original solid is

A

$$\mathrm{Zn(NO_3)_2}$$

B

$$\mathrm{Ca(NO_3)_2}$$

C

$$\mathrm{Al(NO_3)_3}$$

D

$$\mathrm{NaNO_3}$$