A 10.0 W light bulb is used for 5 seconds. How much energy does it consume?

The power of the light bulb ($P$) is $10.0 \text{ W}$.
The time ($t$) for which it uses energy is $5 \text{ seconds}$.

Energy ($E$) is calculated as the product of power ($P$) and time ($t$).

The energy used by the light bulb in 5 seconds is $50 \text{ J}$. This matches option C.

The final answer is $\text{C } \textbf{50 J}$.