Which of these substances has the lowest pH?

Use pH + pOH = 14. For A, pH = 14 − 13.5 = 0.5; for B, pH = 14 − 12.7 = 1.3; and for C, pH = 14 − 2.3 = 11.7. The lowest is 0.5, so 0.5 M HBr has the lowest pH.

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