Match the anion in List I with the observation on warming its solid with conc. $H X_{2} SO X_{4}$ in List II. List I: (P) $Cl X^{-}$ (Q) $Br X^{-}$ (R) $I X^{-}$ (S) $C X_{2} O X_{4} X^{2 -}$ List II: (1) colourless pungent gas giving dense white fumes with a rod dipped in $NH X_{3}$ (2) reddish-brown vapours (3) violet vapours (4) colourless gases, one of which burns with a blue flame

Answer: A

Chloride gives HCl, which forms white

NH X_{4} Cl

fumes with ammonia. Bromide is oxidised to reddish-brown

Br X_{2}

and iodide to violet

I X_{2}

. Oxalate gives CO (blue flame) and

CO X_{2}

. The match is P-1, Q-2, R-3, S-4.