Population density will increase due to:

The correct answer is Option (1) → Natality

The population density of a habitat changes through four basic processes. Two of them add individuals: natality and immigration. Two of them remove individuals: mortality and emigration.

(1) Natality — Correct. It is the number of births in a given period that are added to the initial density of the population.

(2) Emigration — Incorrect. It is the number of individuals of the population that leave the habitat during the period. Density goes down.

(3) Mortality — Incorrect. It is the number of deaths in the population during the period. Density goes down.

(4) Natural disasters — Incorrect. Floods, fires and similar events kill individuals, so they raise mortality and lower the density.

NCERT Extract:
Population Growth – “The size of a population for any species is not a static parameter. It keeps changing with time, depending on various factors including food availability, predation pressure and adverse weather. In fact, it is these changes in population density that give us some idea of what is happening to the population – whether it is flourishing or declining. Whatever might be the ultimate reasons, the density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes, two of which (natality and immigration) contribute to an increase in population density and two (mortality and emigration) to a decrease.”