# What will happen to the pH of a substance if the concentration of hydrogen [H^+] ions increases from 1.0 times 10^-8 to 1.0 times 10^-6?

It will decrease by $2$.
The $\text{pH}$ of solution is defined as -$\log \left(\left[{\text{H}}^{+}\right]\right)$.
For $\left[{\text{H}}^{+}\right] = {10}^{-} 8 ,$ $\text{pH} = 8$
For $\left[{\text{H}}^{+}\right] = {10}^{-} 6 ,$ $\text{pH} = 6$