a
\(\mathrm{HX} \rightleftharpoons \mathrm{H}^{+}+\mathrm{X}^{-} \quad \mathrm{K}_{\mathrm{a}}=1.2 \times 10^{-5}\)

\(0.03 \mathrm{M}\)

\(0.03-\mathrm{x} \quad \mathrm{x} \quad \mathrm{x}\)

\(\mathrm{K}_{\mathrm{a}}=1.2 \times 10^{-5}=\frac{\mathrm{x}^2}{0.03-\mathrm{x}}\)

\(0.03-\mathrm{x} \approx 0.03\left(\mathrm{~K}_{\mathrm{a}}\right. \text { is very small) }\)

\(\frac{\mathrm{x}^2}{0.03}=1.2 \times 10^{-5}\)

\(\mathrm{x}=6 \times 10^{-4}\)

\(\text { Final solution }: 0.03-\mathrm{x}+\mathrm{x}+\mathrm{x}\)

\(=0.03+\mathrm{x}=0.03+6 \times 10^{-4}\)

\(\Pi=\left(0.03+\left(6 \times 10^{-4}\right)\right) \times 0.083 \times 300\)

\(=76.19 \times 10^{-2} \approx 76 \times 10^{-2}\)