d
The ionization reaction for $\mathrm{CH}_{3} \mathrm{COOH}$ follows:
$\mathrm{CH}_{3} \mathrm{COOH} \rightarrow \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{H}^{+}$
At eqm. $\mathrm{x} \quad 3.4 \times 10^{-4} \quad 3.4 \times 10^{-4}$
The ionization constant for the above reaction is written as:
$\mathrm{k}=\frac{\left[\mathrm{CH}_{3} \mathrm{C} \mathrm{OO}^{-}\right]\left[\mathrm{H}^{+}\right]}{\left[\mathrm{CH}_{3} \mathrm{COOH}\right]}$
Putting values in above equation, we get:
$1.7 \times 10^{-5}=\frac{\left(3.4 \times 10^{-4}\right)\left(3.4 \times 10^{-4}\right)}{\mathrm{x}}$
$\mathrm{x}=6.8 \times 10^{-3}$
Hence, option D is correct.