Which lanthanoid compound is used in pigments?

An aqueous solution of $FeSO_4$,$Al_2(SO_4)_3$ and chrome alum is heated with excess of $Na_2O_2$ and filtered. The materials obtained are

$Cu_2Cl_2$ with $HCl$ in the presence of oxidizing agents gives:

Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with $(i)$ iron $(II)$ ions,$(ii)$ $SO_2$,and $(iii)$ oxalic acid? Write the ionic equations for the reactions.

Which one of the following is lunar caustic?

Silver nitrate is mainly used