The Chinese Buddhist pilgrim who visited India during the reign of Chandragupta II was:

The correct answer is B, Fa-Hien. Fa-Hien came to India in search of Buddhist texts and travelled through the Gupta dominions during the reign of Chandragupta II. His account describes a peaceful realm with light punishments, notes that people could travel without passes, records charitable hospitals at Pataliputra, and also reports that Chandalas lived outside towns and had to strike wood to warn others of their approach.

Option A, Hiuen Tsang, came two centuries later in the seventh century, during the reign of Harshavardhana, and studied at Nalanda. Option C, I-tsing, also belongs to the seventh century and wrote about monastic practice in India and the islands of South East Asia. Option D, Megasthenes, was not Chinese at all: he was the Greek ambassador of Seleucus Nicator at the Mauryan court of Chandragupta Maurya and wrote the Indica.