To simplify the expression \( \frac{8}{\sqrt{2}} \), we can multiply the numerator and denominator by \( \sqrt{2} \) to eliminate the square root in the denominator:
\[ \frac{8}{\sqrt{2}} \cdot \frac{\sqrt{2}}{\sqrt{2}} = \frac{8\sqrt{2}}{2} \]
Now, simplify the numerator:
\[ \frac{8\sqrt{2}}{2} = 4\sqrt{2} \]
Therefore, the simplified expression is \( 4\sqrt{2} \).
Looking at the answer options, the correct answer is:
C. \( 4\sqrt{2} \)