100 mL solution of pH = 6 is diluted to 1000 mL. Resulting solution has pH :

${\mathrm{P}}^{\mathrm{H}}=6;\left[{\mathrm{H}}^{+}\right]={10}^{-6}$

${\mathrm{V}}_1=100\mathrm{mL},{\mathrm{V}}_2=1000\mathrm{mL}$

$\left[{\mathrm{H}}^{+}\right] in dilute solution = \left[{\mathrm{H}}^{+}\right] in acid +\left[{\mathrm{H}}^{+}\right] \mathrm{in} \mathrm{water}$

$={10}^{-7}+{10}^{-7}=2\times {10}^{-7}$

$\mathrm{PH}=7-{\log }_{10}^2=7-0.3010=6.79$