The unit used in a pyramid of number is (d) individuals.
Pyramid of number is a type of graphical representation that shows how many number of organisms are present in each trophic level. This pyramid cannot have a constant shape as the the population of each species belonging to a specific trophic level changes from one ecosystem to another. Hence the pyramid can be of three types bases on shape: upright, inverted or partly upright.
Individual is the unit of pyramid of numbers. This is because the pyramid counts the numbers of each individual of a species present in each trophic level.
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