Question

If `pH-=8.25`, what is `[H_3O^+]`?

Answer 1

By definition, `pH=-log_10[H_3O^+]`.........

Explanation:

And thus `[H_3O^+]=10^(-8.25)*mol*L^-1`

`=5.0xx10^-9*mol*L^-1`

With practice, these questions are often trivial. See here for a few details.