The brown ring test is used for the detection of which of the following?

Explain the brown ring test for nitrate ions.

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

The Chromyl chloride test is performed for the confirmation of the presence of which of the following in a mixture?

When salt $BA$ is treated with concentrated $H_2SO_4$, a reddish-brown gas is liberated. The aqueous solution of $BA$ gives a pale yellow precipitate with $AgNO_3$ solution. Which of the following anions $(A^-)$ is present in the salt $BA$?

$A$ sodium salt on treatment with $MgCl_2$ gives white precipitate only on heating. The anion of the sodium salt is