Answer:
endogamy
Explanation:
Endogamy -
It is the method by which the people get married within the similar social groups based on caste is known as endogamy .
This type of practice is very commonly seen in many cultures and religious groups , where people tends to get married within their community , religion and caste .
Since , Sarna married Nathan who is from a different religion , and hence , she has violated the rule of endogamy .