A solution contains $NaNO X_{3}$ and $NaBr$ and a student does the brown ring test directly. A dark brown colour appears at the junction, which cannot be attributed to nitrate alone. Which statements are correct?

AConc. $H X_{2} SO X_{4}$ oxidises $Br X^{-}$ to $Br X_{2}$ .
BThe brown $Br X_{2}$ masks the colour of the ring and gives a false positive.
C $Br X^{-}$ can be removed first by precipitation as AgBr using $Ag X_{2} SO X_{4}$ solution.
D $Br X^{-}$ can be removed first by adding $BaCl X_{2}$ solution.

Answer: A, B, C

Concentrated acid oxidises bromide:

2 Br X^{-} + 2 H X_{2} SO X_{4} Br X_{2} + SO X_{2} + \dots

, and the brown

Br X_{2}

interferes with the ring. Silver sulphate precipitates

Br X^{-}

as AgBr, which is filtered off, so the nitrate test can be done on the filtrate.

BaCl X_{2}

does not precipitate bromide and adds chloride, so statement 4 is false.