Three of the following four are alike in a certain way and so form a group.…

Concept: In a classification-based reasoning question, three of the four items share a common category or property, and the answer is the single item that does not fit that shared category.

Application: Among the four given items, Barley, Wheat, and Rice are cereal grains grown and consumed as staple food. Cotton, in contrast, is a fibre crop grown for its textile fibre and is not consumed as food.

• Barley: an edible cereal grain, used as food and in beverages.

• Cotton: a non-edible fibre crop, grown for textile fibre, not for food.

• Wheat: an edible cereal grain, a staple food crop.

• Rice: an edible cereal grain, a staple food crop.

Cross-check: Barley, Wheat, and Rice all belong to the cereal/food-grain category, confirming they form the alike group; Cotton fits none of these criteria, confirming it is the item that does not belong.

Hence, Cotton is the one that does not belong to the group.