The conductivity and appearance of $CrO_2$ are like metallic $Cu$.

The colorless species is

Indicate the steps in the preparation of:
$(i)$ $K_2Cr_2O_7$ from chromite ore.
$(ii)$ $KMnO_4$ from pyrolusite ore.

On heating potassium permanganate,one of the following compounds is not obtained:

Write about the utility of $d$- and $f$-block elements and their compounds. Or describe the following uses of $d$- and $f$-block elements and their compounds: $(i)$ In iron/steel $(ii)$ As pigments $(iii)$ In batteries $(iv)$ In coinage $(v)$ As catalysts.

The yellow colour solution of $Na_2CrO_4$ changes to orange-red on passing $CO_2$ gas due to the formation of