Which one of the following pairs belongs to the category of primary consumers?

Insects and cattles

The correct answer is (a) Insects and cattle.

Primary consumers are organisms that directly consume producers, which are typically plants or other autotrophic organisms. In the given options, insects and cattle are the only pair that consists of organisms that primarily feed on plants or plant-based materials.

Option (b) Eagle and snakes refers to secondary consumers, as they consume other animals rather than directly feeding on producers.

Option (c) Insects and snakes does not fit the category of primary consumers, as snakes are typically secondary or tertiary consumers that feed on other animals, including insects.

Option (d) Snakes and frogs also does not belong to the category of primary consumers, as frogs can be considered primary consumers themselves, feeding on plants or smaller organisms, while snakes are higher-level consumers that typically prey on other animals.

Therefore, the correct choice is (a) Insects and cattle, as they are both examples of organisms that belong to the category of primary consumers.