# If the hydronium ion concentration of a solution is 1.63 * 10^-8 M, what is the hydroxide ion concentration?

$p H + p O H = 14$, in aqueous solution at $298 K$
If $\left[{H}_{3} {O}^{+}\right] = 1.63 \times {10}^{-} 8$, then $p H = - {\log}_{10} \left(1.63 \times {10}^{-} 8\right)$.
And $\left[H {O}^{-}\right]$ $=$ ${10}^{p H - 14}$, which should be less than $7$. Why so?