Chemistry - Ionic Equilibrium Question with Solution | TestHub

Total volume = 200 mL: $[\mathrm{HA}]=0.1\mathrm{M}$ and $[\mathrm{HB}]=0.05\mathrm{M}$.

$\left[{\mathrm{H}}^{+}\right]=\sqrt{2\times 10^{-5}\times 0.1+4\times 10^{-5}\times 0.05}=\sqrt{4\times 10^{-6}}=2\times 10^{-3}\mathrm{M}$.

$\left[{\mathrm{B}}^{-}\right]=\frac{4\times 10^{-5}\times 0.05}{2\times 10^{-3}}=1\times 10^{-3}\mathrm{M}$.

($\left[{\mathrm{A}}^{-}\right]$ is also $1\times 10^{-3}\mathrm{M}$, so the options with $\left[{\mathrm{H}}^{+}\right]=4\times 10^{-3}$, $\left[{\mathrm{A}}^{-}\right]=2\times 10^{-3}$ and $\left[{\mathrm{B}}^{-}\right]=5\times 10^{-4}$ are wrong.)

Answer: (C).