Menstrual cycle is generally of
(a) 21 days
(b) 28 days
(c) 38 days
(d) 40 days

Options

A. 21 days
B. 28 days
C. 38 days
D. 40 days

Answer

To solve the question regarding the duration of the menstrual cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Menstrual Cycle**: The menstrual cycle is a reproductive cycle that occurs in females, specifically in primates, including humans. It involves a series of physiological changes that prepare the body for potential pregnancy.

2. **Average Duration of the Menstrual Cycle**: The average duration of the menstrual cycle in human females is typically around 28 days. This is the most commonly accepted duration, although it can vary slightly among individuals.

3. **Identifying Ovulation**: Within the menstrual cycle, ovulation occurs approximately on the 14th day. This is when an ovum (egg) is released from the ovary, marking a key event in the cycle.

4. **Evaluating the Options**:
- (a) 21 days: This is shorter than the average menstrual cycle.
- (b) 28 days: This matches the average duration of the menstrual cycle.
- (c) 38 days: This is longer than the average menstrual cycle.
- (d) 40 days: This is also longer than the average menstrual cycle.

5. **Conclusion**: Based on the average duration of the menstrual cycle being approximately 28 days, we can conclude that the correct answer is option (b) 28 days.

### Final Answer:
(b) 28 days