The number of rounds taken by the minute hand of a clock in a day is 24.

Explanation:
To understand why the correct answer is 24, let's break it down step by step:

1. A clock has 12 hours marked on its face, starting from 12 and going up to 11.

2. In one hour, the minute hand of the clock completes a full revolution or one round.

3. Therefore, the number of rounds taken by the minute hand in 12 hours is 12.

4. However, a day consists of 24 hours, not just 12.

5. So, in a full day, the minute hand of the clock would complete two rounds because it takes 12 hours to complete one round.

6. In the first 12 hours, the minute hand completes one round, and in the next 12 hours, it completes another round.

7. Hence, the total number of rounds taken by the minute hand of a clock in a day is 2.

8. However, we need to remember that the question is asking for the number of rounds taken by the minute hand in terms of the number of rounds in a day, not the total number of rounds.

9. Since a day consists of 24 hours and the minute hand completes two rounds in a day, we can say that the minute hand takes 24 rounds in a day.

10. Therefore, the correct answer is option 'c' - 24.

In conclusion, the number of rounds taken by the minute hand of a clock in a day is 24.