Correct option is (B) 10
pOH of a solution is the negative logarithm (where base is 10) of its OH⁻ ion concentration. Therefore,
pOH = -log[OH⁻]
= -log[10-4]
= 4
We know,
pH + pOH = 14
⇒ pH + 4 = 14
∴ pH = 10
Therefore, the pH of 10-4 M NaOH solution is 10.
