The rate of natural increase of a population refers to the difference…

The correct answer is Option (4) → The birth rate and the death rate

Option (1) The fertility rate and the replacement rate — Incorrect. The replacement rate is the growth needed for new generations to replace the older ones dying out. A population reaches it when the rate of natural increase is zero or very small.

Option (2) The fertility rate and the death rate — Incorrect. The fertility rate counts births per 1000 women of child-bearing age. Natural increase uses the birth rate, worked out on the whole population, so the fertility rate is the wrong measure here.

Option (3) The birth rate and the infant mortality rate — Incorrect. The infant mortality rate counts only the deaths of babies before their first birthday. Natural increase must take away all deaths, so it needs the full death rate.

Option (4) The birth rate and the death rate — Correct. The rate of natural increase, also called the growth rate of population, is the birth rate minus the death rate. Both are counted per 1000 population, so one can be taken from the other.