Assertion : Migration is an important factor which determines both population size and population density.
Reason : In migration, a major part of population goes from one area to another area.

Options

A. If both Assertion and Reason are true and Reason is a correct explanation of Assertion.
B. If both Assertion and Reason are true and Reason is not a correct explanation of Assertion.
C. If Assertion is true but Reason is false
D. If both Assertion and Reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Migration is an important factor which determines both population size and population density."
- **Population Size** refers to the total number of individuals in a population.
- **Population Density** is the number of individuals per unit area or volume.

2. **Understanding the Reason**:
- The reason states that "In migration, a major part of the population goes from one area to another area."
- This means that migration involves the movement of individuals from one location to another, which can affect both how many individuals are present in a given area (population size) and how crowded that area is (population density).

3. **Evaluating the Assertion and Reason**:
- Both statements are true. Migration can indeed influence population size by increasing or decreasing the number of individuals in a specific area. It also affects population density as the movement of individuals alters how many are present in a given space.

4. **Determining the Relationship**:
- The reason provided correctly explains the assertion. If a significant number of individuals migrate to or from an area, it will directly impact the population size and density in that area.

5. **Conclusion**:
- Since both the assertion and reason are true, and the reason is a correct explanation of the assertion, the correct answer is that both the assertion and reason are true, and the reason is a correct explanation of the assertion.

### Final Answer:
The correct option is: **Both assertion and reason are true, and reason is a correct explanation of assertion.**

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