(i)
Potassium dichromate ($K_{2}C{r}_2{O}_7$ ) is prepared from chromite ore$\left(FeC{r}_2{O}_4\right)$ in the
following steps.

Step (1): Preparation of sodium chromate

$4FeC{r}_2{O}_4+16Na\mathrm{OH}+ 7O_2 \to 8N{a}_{2}Cr{O}_4+2F{e}_2{O}_3+8H_{2}O$
$$

Step (2): Conversion of sodium chromate into sodium dichromate

$2N{a}_{2}Cr{O}_4+conc.H_{2}S{O}_4\to N{a}_{2}C{r}_2{O}_7+N{a}_{2}S{O}_4+H_{2}O$
$$

Step(3): Conversion of sodium dichromate to potassium dichromate

\(\mathrm{Na}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+2 \mathrm{KCl} \rightarrow \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+2 \mathrm{NaCl}\)

Potassium chloride is less soluble than sodium chloride is obtained in the form of

orange colored crystals and can be removed by filtration.

(ii)

Potassium permanganate is prepared by fusion of MnO₂ with an alkali metal hydroxide and an oxidizing agent like KNO₃ .
This produces the dark green K₂MnO₄ which disproportionates in a neutral or acidic solution to give permanganate. 

The reaction is as follows:


2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O
3MnO₄^2– + 4H⁺ → 2MnO₄^– + MnO₂ + 2H₂O