Question

${Fe}^{2+}$ does not give blue colour with $K_4\left[{Fe\left(CN\right)}_6\right]$, but on its reaction with (X), blue colour appears. (X) can be :

• A. ${MnO}_4^{-}/H^{+}$
• B. $H_2{SO}_4$
• C. ${NH}_3$
• D. $HCl$

Answer 1

The correct option is A ${MnO}_4^{-}/H^{+}$

F(II) ions give white precipitate of ferrous ferricyanide $\left(F{e}_2\right[Fe\left(CN{)}_6\right]$ with potassium ferrocyanide.
F(III) ions give deep blue colour with potassium ferrocyanide.

$3K_4\left[Fe\right(CN{)}_6]+4FeC{l}_3\to \underset{purssianblue}{F{e}_4\left[Fe\right(CN{)}_6{]}_3}+12KCl$

Potassium permanganate is a strong oxidizing agent. In acidic medium, it oxidzes Fe(II) ions to Fe(III) ions which then react with potassium ferrocyanide to give deep blue colour.

Option A is correct.