Answer: Kshatriyas
In Nectar in a Sieve, Rukmani is a member of the Kshatriyas caste.
The Kshatriya is one of the four varna (social classes) of Hindu society. This usually includes the ruling and military class. In the novel, we know that Rukamni's father was an important man. However, he could not afford to pay a large dowry. Therefore, Rukmani is married to Nathan, a simple farmer. Nevertheless, she loves him and is mostly happy in her marriage.