The correct answer is Option 3- Ashoka

The Mauryan ruler who became a follower of Buddhism was Ashoka. He was the third emperor of the Mauryan Empire, and he ruled from 272 to 232 BCE. Ashoka was initially a follower of Hinduism, but he converted to Buddhism after the Kalinga War in 261 BCE. The Kalinga War was a bloody conflict that left over 100,000 people dead. Ashoka was deeply troubled by the bloodshed, and he turned to Buddhism in search of peace and non-violence. As a Buddhist, Ashoka promoted the spread of Buddhism throughout his empire and beyond. He sent missionaries to Sri Lanka, Central Asia, and Southeast Asia. He also built Buddhist monasteries and stupas. Ashoka's patronage of Buddhism helped to make it one of the major religions of the world.

Other options:

Samudragupta was the third Gupta emperor (Hindu), who ruled from 335 to 375 CE.

Brihadratha was the last Mauryan emperor, who was killed by his general Pushyamitra Shunga in 185 BCE.

Chandragupta was the founder of the Mauryan Empire, and he became a follower of Jainism.