Describe the chemical reactions of the lanthanoids with $H_2$ and $O_2$.

The incorrect statement$(s)$ among $(a)-(c)$ is (are) :-
$(a)$ $W(VI)$ is more stable than $Cr(VI)$
$(b)$ In the presence of $HCl$,permanganate titrations provide satisfactory results.
$(c)$ Some lanthanoid oxides can be used as phosphors.

Assertion $(A):$ $VF_5$ is stable while $VCl_5$ is not.
Reason $(R):$ Fluorine stabilizes the higher oxidation state due to its higher bond enthalpy.
The correct option among the following is

Give examples and suggest reasons for the following features of the transition metal chemistry:
$(i)$ The lowest oxide of transition metal is basic,the highest is amphoteric/acidic.
$(ii)$ $A$ transition metal exhibits highest oxidation state in oxides and fluorides.
$(iii)$ The highest oxidation state is exhibited in oxoanions of a metal.

Which of the following will not form an amalgam?

Ferrous sulphate on heating gives