Assertion: Natality rate increases both population size and population density.
Reason: Natality increases the number of individuals in an area by births.

Options

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

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Assertion:** The assertion states that the natality rate increases both population size and population density. Natality refers to the birth rate within a population.

2. **Defining Natality:** Natality is generally expressed as the number of births per thousand individuals in a population per year. It is a measure of how many new individuals are added to a population through reproduction.

3. **Impact on Population Size:** When the natality rate increases, it means that more individuals are being born in a given area. This directly contributes to an increase in the overall population size, as the total number of individuals in that population rises.

4. **Impact on Population Density:** Population density is defined as the number of individuals per unit area. As the population size increases due to higher natality, the population density also increases, assuming the area remains constant.

5. **Understanding the Reason:** The reason provided states that natality increases the number of individuals in an area by births. This is a direct explanation of how natality affects both population size and density.

6. **Conclusion:** Since both the assertion and the reason are true, and the reason correctly explains the assertion, we conclude that the correct option is: "If both assertion and reason are true, the reason is the correct explanation of the assertion."