The correct answer is C. 1,00,000.
Population equivalent (PE) is a measure of the amount of organic waste produced by a population. It is calculated by multiplying the BOD of a town by the population of the town and dividing by the BOD per capita per day.
In this case, the BOD of the town is 20000 kg/day, the population of the town is unknown, and the BOD per capita per day is 0.05 kg. Therefore, the PE of the town is:
PE = 20000 kg/day * population of town / 0.05 kg/day/person = 400000 people
Since the population of the town is unknown, the PE can only be estimated. However, the PE of a town is typically in the range of 1000 to 100000 people. Therefore, the PE of the town in this case is most likely 1,00,000 people.
Option A is incorrect because the PE of a town is typically in the range of 1000 to 100000 people, and 1000 is less than 1000.
Option B is incorrect because the PE of a town is typically in the range of 1000 to 100000 people, and 4000 is less than 10000.
Option D is incorrect because the PE of a town is typically in the range of 1000 to 100000 people, and 400000 is greater than 100000.