200mL of 0 . 01MHCl is mixed with 400mL of 0 . 01 MH _ 2 SO _ 4 ....

pH of a mixture of $HCl + {H}_{2}{SO}_{4}$ has to calculated

The number of equivalents of HCl is equal to $0 . 02equivalents$

The number of equivalents of ${H}_{2}{SO}_{4}$ given is equal to $0 . 008$ equivalents

Hydrogen ion concentration of the resultant mixture is equal to$\left[{H}^{+}\right] = \dfrac{\left(0 . 01 \times 200\right) + \left(0 . 01 \times 2 \times 400\right)}{600}$

$= \dfrac{2 + 8}{600} = \dfrac{10}{600} = \dfrac{1}{60}$

$pH = - \log \left[\dfrac{1}{60}\right]$

$= 1 . 78$