$10 = {P^0} \times 0.2$ ;
$20 = {P^0} \times n$ $ \Rightarrow $ $n = 0.4$ $N = 0.6$.
$(i)$ $0.10\, {M} \,{Ba}_{3}\left({PO}_{4}\right)_{2}$
$(ii)$ $0.10\, {M}\, {Na}_{2} {SO}_{4}$
$(iii)$ $0.10\, {M}\, {KCl}$
$(iv)$ $0.10 \,{M} \,{Li}_{3} {PO}_{4}$