Which of the following is used as a white pigment?

Which of the following melts in boiling water?

$MnO_2$ when fused with $KOH$ and oxidised in air gives a dark green compound $X$. In acidic solution,$X$ undergoes disproportionation to give an intense purple compound $Y$ and $MnO_2$. The compounds $X$ and $Y$,respectively,are

Potassium manganate $(K_2MnO_4)$ is not formed in which of the following reactions?

Identify the correctly matched pairs:
$(i)$ $TiO_2$ - pigment industry
$(ii)$ $MnO_2$ - dry battery cells
$(iii)$ $Cu/Ni$ alloy - $UK$ 'copper' coins

Which one of the following statements is correct when $SO_2$ is passed through acidified $K_2Cr_2O_7$ solution?