The population reaches replacement level when growth rate is :

zero

The correct answer is Option (1) - zero

The rate of natural increase or the growth rate of population refers to the difference between the birth rate and the death rate. When this difference is zero (or, in practice, very small) then we say that the population has ‘stabilised’, or has reached the ‘replacement level’, which is the rate of growth required for new generations to replace the older ones that are dying out.