What will be the $pH$ of a $10^{-8} \ M \ HCl$ solution?

The $pH$ of $1 \ N$ $KOH$ solution is:

The $pH$ of a $10^{-8} \ M \ HCl$ aqueous solution is ......

$x \ mg$ of $Mg(OH)_2$ (molar mass $= 58 \ g/mol$) is required to be dissolved in $1.0 \ L$ of water to produce a $pH$ of $10.0$ at $298 \ K$. The value of $x$ is $........... mg$ ($Nearest$ $integer$). ($Given$: $Mg(OH)_2$ is assumed to dissociate completely in $H_2O$)

What is the $pH$ of a solution containing $H^{+}$ ion concentration $2.5 \times 10^{-3} \ mol \ dm^{-3}$? (Given $\log 2.5 = 0.3979$)

Water is added to $1.0 \ mL$ of $0.1 \ M$ $HCl$ solution to make the total volume $50 \ mL$. Calculate the $pH$ change of the solution.