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CLEP chemistry-aligned problems require facility with logarithms and acid–base definitions. pH is defined as −log⁡10[H+]-\log_{10}[\mathrm{H}^+]. Compute log⁡10(2.5×10−4)=log⁡10(2.5)+log⁡10(10−4)=0.39794−4=−3.60206\log_{10}(2.5\times10^{-4})=\log_{10}(2.5)+\log_{10}(10^{-4})=0.39794-4=-3.60206. Taking the negative gives 3.602063.60206, so pH ≈ 3.60 (choice A). Because the acid is strong and the concentration is sufficiently large, we treat [H+][\mathrm{H}^+] as equal to the formal concentration, neglecting autoionization of water. Option B (4.40) results from mistakenly subtracting rather than adding the mantissa; option D (0.40) ignores the exponent; option C (10.40) confuses pH with pOH or misapplies the pH+pOH=14\mathrm{pH}+\mathrm{pOH}=14 relation. CLEP objectives emphasize interpreting scientific notation, significant figures, and log rules (e.g., log⁡ab=log⁡a+log⁡b\log ab=\log a+\log b). Also note qualitative interpretation: a pH near 3.6 indicates an acidic solution (pH<7). Comfort with logs supports related topics such as pKapK_a, buffer calculations (Henderson–Hasselbalch), and titration curves.