Which of these substances has the highest pOH?

At 25°C, pH + pOH = 14, so pOH = 14 − pH. For 0.10 M HCl, pOH = 14 − 1 = 13; for HNO₃, it is 11; and for NaOH, it is 2. Therefore, 0.10 M HCl has the highest pOH.

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