A society permits marriage only within one's own social group but allows complete freedom in occupation, food-sharing and social interaction. Which defining feature of caste is most clearly present in this society?

Endogamy

The correct answer is Option 3: Endogamy.

Endogamy refers specifically to restrictions on marriage requiring individuals to marry within their own group. The other features may or may not be present, but the information provided directly establishes endogamy.