Answer
$[H_3O^+] = 1.26 \times 10^{- 8}M$
Work Step by Step
$[H_3O^+] = 10^{-pH}$
$[H_3O^+] = 10^{- 7.90}$
$[H_3O^+] = 1.26 \times 10^{- 8}M$
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