Which of the following scenarios would lead to a decrease in population density in a given habitat?

Both the death rate and the emigration rate are high.

The correct answer is Option (3) - Both the death rate and the emigration rate are high.

(a) Natality > mortality: If the birth rate (natality) is higher than the death rate (mortality), it means that more individuals are being born into the population than are dying. This would lead to an increase in population density rather than a decrease, as the population is growing.

(b) Immigration > emigration: When more individuals are moving into the habitat through immigration than leaving it through emigration, it would result in an increase in population density. This is because the number of individuals in the population is increasing due to immigration.

(c) Mortality and emigration: If both the death rate (mortality) and the emigration rate are high, it means that a significant number of individuals are dying and leaving the habitat. This would result in a decrease in population density, as the population is decreasing due to both factors.

(d) Natality and immigration: If both the birth rate (natality) and the immigration rate are high, it means that more individuals are being born and more individuals are moving into the habitat. This would also lead to a increase in population density, as the population is  being replenished by new births or immigration.

In summary, options (3)  would necessarily decrease the density of a population in a given habitat.