The Hydrogen Potential $\mathrm { pH }$ , of a Substance Is Defined By

The hydrogen potential, $\mathrm { pH }$ , of a substance is defined by $\mathrm { pH } = - \log \left[ \mathrm { H } ^ { + } \right]$ , where $\left[ \mathrm { H } ^ { + } \right]$ is measured in moles per liter. Find the pH of a sample of lake water whose $\left[ \mathrm { H } ^ { + } \right]$ is $3.05 \times 10 ^ { - 9 }$ moles per liter. (Round to the nearest tenth.)

A) 7.3
B) 10.1
C) 8.5
D) 6.4