The value of lo g_10 ( 0.0001 ) is = ?

Answer: Option C

$$\begin{array}{rl}& \text{lo}{\text{g}}_{10}\left(0.0001\right)\\ & =\text{lo}{\text{g}}_{10}\left(\frac{1}{10000}\right)\\ & =\text{lo}{\text{g}}_{10}\left(\frac{1}{{10}^4}\right)\\ & =\text{lo}{\text{g}}_{10}10^{-4}\\ & =-4\text{lo}{\text{g}}_{10}10\\ & =-4\end{array}$$