A colourless salt Y dissolves in water. It gives no precipitate with $BaCl X_{2}$ in the presence of dilute HCl, evolves a gas that turns moist red litmus blue on warming with NaOH, and gives a canary-yellow precipitate with ammonium molybdate and concentrated $HNO X_{3}$ . Y and the oxidation state of Mo in the yellow precipitate are respectively

Answer: B

The gas with NaOH is

NH X_{3}

(so ammonium is present), the yellow precipitate shows phosphate, and the absence of a

BaCl X_{2}

/HCl precipitate rules out sulphate. Hence Y is

(NH X_{4}) X_{2} HPO X_{4}

and not

Na X_{2} HPO X_{4}

(NH X_{4}) X_{2} SO X_{4}

. In the phosphomolybdate, molybdenum stays

+ 6

because the reaction is not a redox reaction.