Select the correct statements :

(P) pH of ${\mathrm{NaHCO}}_3$ solution can be given by:

$\frac{p{K}_{{\mathrm{H}}_2{\mathrm{CO}}_3}+p{K}_{{\mathrm{HCO}}_3^{-}}}{2}$

(Q) ${\mathrm{Al}}^{3+}\text{ ion }$is amphoteric

$\text{ (R) }{K}_{sp}$ values of metal nitrate are very-very high

(S) Na+(aq) is conjugate acid of NaOH(aq).