Assertion: Two regions with identical population sizes may have very different demographic characteristics.

Reason: Population composition includes attributes such as age and sex structure.

Both Assertion and Reason are true, and Reason correctly explains Assertion.

The correct answer is Option 1: Both Assertion and Reason are true, and Reason correctly explains Assertion.

Assertion: Two regions with identical population sizes may have very different demographic characteristics. Correct. Population size alone does not reveal the characteristics of a population. Two regions with the same number of people may differ significantly in age structure, sex ratio, literacy, dependency ratio, and other demographic features.

Reason: Population composition includes attributes such as age and sex structure. Correct. Population composition refers to the characteristics of a population, including age structure, sex composition, literacy, occupation, and other demographic attributes.

How the Reason explains the Assertion: The Reason correctly explains the Assertion because differences in population composition can exist even when total population size is identical. Since age structure and sex composition are important demographic characteristics, two populations of the same size can still have very different demographic profiles.