Natality refers to

The correct option is B Birth rate
Natality refers to the number of births during a given period in the population that are added to the initial density. It is used to express birth rate.
Mortality is the number of deaths in the population during a given period. It is used to express death rate.
Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.