Carbonic acid, ${\mathrm{H}}_2{\mathrm{CO}}_3$, is a diprotic acid for which $K_1=4.2\times {10}^{-7}$ and $K_2=4.7\times {10}^{-11}$ Which solution will produce a pH closest to 9?

The solution will produce a pH closest to 9. The formula to calculate the pH value,

$\mathrm{pH}=\frac{p{k}_1+p{k}_2}{2}~9$

Here, the solution of $0.1 \mathrm{M} {\mathrm{NaHCO}}_3$ gives the value of pH near 9.