How many hydrogen ions are present in 1 ml of a solution of pH = 13 ?

pH = 13

$$\begin{gathered} -\log \left[{\mathrm{H}}^{+}\right] = 13 \\ \mathrm{or} \left[{\mathrm{H}}^{+}\right] ={10}^{-13} \mathrm{mole}/\mathrm{litre} \\ \left[{\mathrm{H}}^{+}\right] \mathrm{in} 1 \mathrm{ml} = {10}^{-16} \mathrm{moles} \\ 1 \mathrm{mole} {\mathrm{H}}^{+} \mathrm{contains} 6.023 \times {10}^{23} {\mathrm{H}}^{+} \mathrm{ions} \\ \therefore \mathrm{No}. \mathrm{of} {\mathrm{H}}^{+} \mathrm{ions} \mathrm{in} {10}^{-16} \mathrm{moles} \\ = 6.023 \times {10}^{23} \times {10}^{-16} = 6.023 \times {10}^7 \end{gathered}$$