Answer
$[H_3O^+] = 1.61 \times 10^{- 14}M$
Work Step by Step
1. Since NaOH is a strong base:
$[OH^-] = [NaOH] = 0.62M$
2. Calculate [$H_3O^+$] using $[OH^-]$
$[OH^-] * [H_3O^+] = Kw = 10^{-14}$
$ 0.62 * [H_3O^+] = 10^{-14}$
$[H_3O^+] = \frac{10^{-14}}{ 0.62}$
$[H_3O^+] = 1.61 \times 10^{- 14}$
