How many litres of water must be added to I L of an aqueous solution with a pH of 1 to create an aqueous solution of pH of 2?

$\mathrm{pH}=1 \therefore \left[{\mathrm{H}}^{+}\right]={10}^{-1}=0.1\mathrm{M}$

$\mathrm{pH}=2 \therefore \left[{\mathrm{H}}^{+}\right]={10}^{-2}=0.01\mathrm{M}$

$\text{ For dilution of }\mathrm{HCl}: {\mathrm{M}}_1{\mathrm{V}}_1={\mathrm{M}}_2{\mathrm{V}}_2$

$0.1\times 1=0.01\times {\mathrm{V}}_2$

${\mathrm{V}}_2=10 \mathrm{L}$

Volume of water to be added = 10-1 = 9L