A solution is prepared by mixing 0.01 mol of each of ${\mathrm{H}}_2{\mathrm{CO}}_3, {\mathrm{NaHCO}}_3,{\mathrm{Na}}_2{\mathrm{CO}}_3$ and $\mathrm{NaOH}$ in 100 ml of water  ${\mathrm{P}}^{\mathrm{H}}$ of resulting solution is nearly _______.
$[\mathrm{P}{\mathrm{ka}}_1\mathrm{and}{\mathrm{Pka}}_2\mathrm{of}{\mathrm{H}}_2{\mathrm{CO}}_3$ are 6.37 and 10.31 respectively.  $\log 2=0.3010]$ 

$H_{2}C{O}_3+NaOH\to NaHC{O}_3+H_{2}O$

Millimole             10                  10                 -                    -
At end                   0                   0                  10+10=20.
$\Rightarrow$Final mixture has 20 milli moles $NaHC{O}_3$and 10 millimoles $N{a}_{2}C{O}_3$

$P^H=Pk{a}_2+\log \frac{salt}{Acid}[Buffer:N{a}_{2}C{O}_3+NaHC{O}_3]$

$P^H=10.31+\log \left(\frac{10}{20}\right)$

$\approx 10$