A country records exactly the same number of births and deaths in a particular year. Which conclusion necessarily follows?

The rate of natural increase is zero.

The correct answer is Option 1: The rate of natural increase is zero.

Natural increase is calculated as the difference between births and deaths. If the number of births and deaths is exactly the same, the rate of natural increase becomes zero. 

Option 1: The rate of natural increase is zero. Correct. When births equal deaths, the natural increase (births − deaths) is zero.

Option 2: The country has entered the final stage of demographic transition. Incorrect. Equal births and deaths alone do not reveal the stage of demographic transition. A country in different stages may temporarily record equal numbers of births and deaths (more deaths due to an epidemic).

Option 3: The country has achieved replacement-level fertility. Incorrect. Replacement-level fertility refers to the average number of children needed for one generation to replace itself. It cannot be determined merely from one year's birth and death figures.