The phosphate radical reacts with ammonium molybdate to form a precipitate of which color?

Anion which can react with $dil. H_2SO_4$ is

$A$ brown ring appears in the test for

$A$ salt gives violet vapours when treated with conc. $H_2SO_4$. It contains

$A$ chloride salt solution acidified with dil. $HNO_3$ gives a curdy white precipitate,$[A]$,on addition of $AgNO_3$. $[A]$ on treatment with $NH_4OH$ gives a clear solution,$B$. Identify $[A]$ and $B$.

$[X] + H_2SO_4 \rightarrow [Y]$ (a colorless gas with a pungent smell). $[Y] + K_2Cr_2O_7 + H_2SO_4 \rightarrow$ green solution. What are $[X]$ and $[Y]$?