Final answer:
The state of ultimate peace in Buddhism, achieved by the extinction of all desire, is called nirvana. It signifies complete liberation and enlightenment, distinct from the continuous cycle of rebirth known as Samsara. Option a is the answer.
Step-by-step explanation:
Buddhists call the state of ultimate peace found in the extinction of all desire nirvana. This is a state beyond suffering and the cycle of rebirth, representing complete liberation from the karmic cycle of death and rebirth. Nirvana is the ultimate goal for Buddhists, where one is freed from all forms of desire and reaches a state of enlightenment, as taught by the Buddha after he attained it himself. It's not to be confused with Samsara, which is the continuous cycle of life, death, and rebirth, from which Buddhists seek to escape.