A green solution of salt X gives a grey-green precipitate with $NH X_{4} Cl / NH X_{4} OH$ . The precipitate, warmed with $NaOH$ and $H X_{2} O X_{2}$ , gives a yellow solution that yields a yellow precipitate with lead acetate in acetic acid. The cation in X and the moles of $H X_{2} O X_{2}$ consumed per mole of cation oxidised are

Answer: C

Grey-green hydroxide and yellow

PbCrO X_{4}

show chromium.

Cr X^{3 +} \to CrO X_{4} X^{2 -}

releases 3 electrons per Cr, and each

H X_{2} O X_{2}

accepts 2 electrons, so

3/2 = 1.5

mol

H X_{2} O X_{2}

per mole Cr, consistent with

2 Cr (OH) X_{3} + 3 H X_{2} O X_{2} + 4 OH X^{-} 2 CrO X_{4} X^{2 -} + 8 H X_{2} O