Which of the following is a synonym of acceleration?

The synonym of acceleration is:

ক) Hastening

Explanation:
- Acceleration means an increase in speed or the act of moving faster.
- Hastening also means speeding up or making something happen more quickly.
- The other options are opposite in meaning:

- Slackening means to slow down or become less intense.
- Braking refers to the act of slowing down or stopping.
- Slowing down is the direct opposite of accelerating.

Thus, the correct synonym is hastening (ক).