Homologous organs are those which are functionally similar but different by origin.
Homothallic plants are those which are unisexual.

Options

A. If both A and R are correct and R is correct explanation of A
B. If both A and R are correct but R is not correct explanation of A
C. If A is correct, R is wrong
D. If both A and R are wrong.

Answer

### Step-by-Step Solution

1. **Understanding the Assertion**: The assertion states that "homologous organs are those which are functionally similar but different by origin."
- **Analysis**: Homologous organs actually have a common origin but may serve different functions. For example, the forelimbs of humans and bats are homologous because they share a common evolutionary origin, even though they perform different functions (manipulation vs. flight).

2. **Conclusion on Assertion**: The assertion is incorrect because it misdefines homologous organs. They are not functionally similar; they are functionally different.

3. **Understanding the Reason**: The reason states that "homothallic plants are those which are unisexual."
- **Analysis**: Homothallic plants are actually those that have both male and female reproductive structures on the same plant, making them bisexual. In contrast, unisexual plants have either male or female structures, but not both on the same plant.

4. **Conclusion on Reason**: The reason is also incorrect because it incorrectly defines homothallic plants as unisexual.

5. **Final Conclusion**: Both the assertion and the reason are incorrect. Therefore, the correct option is that both the assertion and the reason are false.