Which of the following examples represents a population? 

All of these

The correct answer is (d) All of these.

a-Bacteria in a culture plate

b-Rats living in an abandoned dwelling 

c-A teakwood tree in a forest tract 

All of the given examples represent populations. A population refers to a group of organisms of the same species that live in a specific geographical area and share similar resources.

• Bacteria in a culture plate form a population as they are a group of bacteria of the same species living in a confined space and sharing the same growth medium.
• Rats living in an abandoned dwelling form a population as they are a group of rats of the same species living in a specific habitat.
• A teakwood tree in a forest tract represents a population as it is an individual tree of a specific species in a particular area where other teakwood trees of the same species may also be present.

In each case, the organisms belong to the same species and are interacting with each other and their environment as a population.