What is the pOH of a solution that has a hydroxide ion concentration of a 0.01 M HCl solution?

Method 1 :

HCl is a strong acid which is completely ionized in aqueous solution to form H⁺ ions.
Hence, [H⁺] of 0.01 M HCl solution = 0.01 M

pH = -log[H⁺] = -log(0.01) = 2.0
pOH = pKw - pH = 14.0 - 2.0 = 12.0


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Method 2 :

HCl is a strong acid which is completely ionized in aqueous solution to form H⁺ ions.
Hence, [H⁺] of 0.01 M HCl solution = 0.01 M

[OH⁻] = Kw / [H⁺] = (1.0 × 10⁻¹⁴) / 0.01 M = 1.0 × 10⁻¹² M
pOH = -log[OH⁻] = -log(1.0 × 10⁻¹²) = 12.0