# If a solution has a [H^+] concentration of 4.5 * 10^-7 M, is this an acidic or basic solution?

The solution is acidic inasmuch as $p H < 7$.
In water, acidity is measured by the logarithmic function $p H$, where $p H$ $=$ $- {\log}_{10} \left[{H}_{3} {O}^{+}\right]$.
So $- {\log}_{10} \left(4.5 \times {10}^{-} 7\right)$ $=$ $6.35$. This is slightly acidic as anticipated.