Step 1: Convert the percentage.
0.04 % means 0.04 parts in 100, so $\alpha = 4\times10^{-4}$.
Step 2: Use the equilibrium.
HA $\rightleftharpoons$ H$^+$ + A$^-$. Moles dissociated per litre = $C\alpha$, so $[\text{H}^+] = 0.25 \times 4\times10^{-4}$.
Step 3: Calculate.
\[ [\text{H}^+] = 1.0\times10^{-4}\text{ M}, \quad \text{pH} = 4 \]
Step 4: Sanity check.
A weak acid must give pH below 7. Option (D) with pH 10 is basic and impossible. Options (A) and (C) do not match $10^{-4}$ M.
Final Answer:
The pH of the solution is 4.
\[ \boxed{4} \]