[A]: The endosperm contains the triploid number of chromosomes.
[R]: The endosperm is formed as a result of fusion of two polar nuclei and one of the male nuclei

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To analyze the given statement regarding the endosperm in plants, we will break down the assertion and reason step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "The endosperm contains the triploid number of chromosomes."
- In plants, the endosperm is a tissue that provides nutrition to the developing embryo. It is formed during fertilization and is characterized by having three sets of chromosomes, which is referred to as triploid (3N).

2. **Understanding the Reason**:
- The reason states that "The endosperm is formed as a result of fusion of two polar nuclei and one of the male nuclei."
- During the process of double fertilization in angiosperms (flowering plants), one male gamete (pollen) fuses with the egg cell to form the zygote (diploid), while the other male gamete fuses with the two polar nuclei (which together are diploid) to form the primary endosperm nucleus (PEN), which is triploid.

3. **Connecting Assertion and Reason**:
- The assertion is true because the endosperm indeed has a triploid number of chromosomes (3N).
- The reason is also true because it accurately describes the process by which the endosperm is formed (fusion of two polar nuclei and one male nucleus).

4. **Determining the Relationship**:
- Since both the assertion and reason are true, and the reason correctly explains the assertion, we conclude that the reason is a correct explanation of the assertion.

5. **Final Conclusion**:
- Therefore, the correct answer is: Both assertion and reason are true, and the reason is the correct explanation of the assertion.

### Answer:
The correct option is: **If both assertion and reason are true and reason is the correct explanation of the assertion.**

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