Which of the following options does not involve using relative density as a measure of population density in a certain area?

Both options (a) and (c)

a-Assessing the population density of tigers in a forest by counting their pugmarks.

b-Determining the population density of fishes in a lake by counting the number of fishes caught in a trap.

c-Estimating the population density of bacteria in a petri dish by measuring the biomass of a bacterial culture.

d-Both options (a) and (c) 

Option (d) is indeed the correct answer. Both options (a) and (c) are not examples of using relative density to measure population density in a certain area.

Relative density is a measure that provides information about the proportion or relative abundance of individuals in a population without directly counting the actual number of individuals. Instead, it relies on observable indicators or indirect estimation methods.

Option (a), counting pug marks of tigers, is an example of an indirect estimation method used in tiger census. It provides information about the presence and distribution of tigers in a forest, but it does not give a direct count of the actual number of individuals.

Option (c), measuring the biomass of a bacterial culture, is also not an example of using relative density. It is a measure of the total biomass or the weight of the bacterial population in a given area, which indirectly reflects the population density of bacteria.

Therefore, the correct answer is option (d) - Both options (a) and (c) are not examples of using relative density to measure population density in a certain area.