In a laboratory population of 80 fruit flies, 8 died in a week, then the death rate of fruit flies is:

0.1 individuals per fruit fly per week

The correct answer is Option (3) → 0.1 individuals per fruit fly per week

A population has certain attributes whereas, an individual organism does not. An individual may have births and deaths, but a population has birth rates and death rates. In a population these rates refer to per capita births and deaths. The rates, hence, expressed are change in numbers (increase or decrease) with respect to members of the population.

If 8 fruitflies in a laboratory population of 80 fruitflies die in a week then the death rate of fruit flies is 8/80 = 0.1 individuals per fruitfly per week.

Death rate = (Number of deaths) / (Total population)

In this case:

Death rate = 8 deaths / 80 fruit fly

Death rate = 0.1 deaths per fruit fly per week