Step 1: Evaluating the Assertion (A):
During colonial rule, the British administration classified various Indian communities into rigid, generalized categories. They labeled certain groups (like Sikhs, Gurkhas, and Pathans) as "martial races" suited for military service, and others (like the trading communities or some tribal groups) as "effeminate", "cowardly", or "untrustworthy" (e.g., under the Criminal Tribes Act of 1871). This statement is historically accurate and thus True.
Step 2: Evaluating the Reason (R):
In sociological theory, a stereotype is defined as a highly simplified, rigid, and inflexible characterization applied to an entire group of people, completely disregarding individual differences. This definition is academically accurate and thus True.
Step 3: Evaluating the Logical Link:
The British classification of Indian communities into "martial", "cowardly", or "untrustworthy" races is a classic, concrete historical manifestation of stereotyping. They applied rigid, generalized characteristics to diverse populations. Since the Assertion presents a specific historical example and the Reason defines the underlying sociological concept that perfectly explains it, (R) is the correct explanation of (A).