To find Usain Bolt's speed as a unit rate, we can use the formula for speed, which is:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
In this case, the distance is 100 meters and the time is 9.63 seconds.
Now we can calculate his speed:
\[ \text{Speed} = \frac{100 \text{ meters}}{9.63 \text{ seconds}} \approx 10.4 \text{ meters per second} \]
Rounding to the nearest tenth, Usain Bolt's speed during the 2012 Olympics was 10.4 meters per second. Therefore, the correct answer is:
10.4 meters per second.