JEE Advanced 2021 Paper 2

Paragraph for next 2 questions The reaction of ${K}_{3}[ {Fe}( {CN})_{6}]$ with freshly prepared ${FeSO}_{4}$ solution produces a dark blue precipitate called Turnbull's blue. Reaction of ${K}_{4}[ {Fe}( {CN})_{6}]$ with the ${FeSO}_{4}$ solution in complete absence of air produces a white precipitate $X$, which turns blue in air. Mixing the ${FeSO}_{4}$ solution with ${NaNO}_{3}$, followed by a slow addition of concentrated ${H}_{2} {SO}_{4}$ through the side of the test tube produces a brown ring.