Answer
$pH\approx 7.5$,
the substance is basic
Work Step by Step
(see p.381)
The $\mathrm{p}\mathrm{H}$ scale measures the acidity of a solution:$ \quad \mathrm{p}\mathrm{H}=-\log[\mathrm{H}^{+}]$
where $[\mathrm{H}^{+}]$ is the hydrogen ion concentration (in moles per liter, M).
Solutions are
neutral if $pH = 7$
acidic if $pH < 7$
basic if $pH > 7$
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$pH=-\log[\mathrm{H}^{+}]=-\log(3.1\times 10^{-8})\approx 7.5 > 7,$ basic