The correct answer for the foreign traveler who visited India during the Vijayanagara period is option 4 - Nicolo Conti.

1. Megasthenes: Megasthenes was a Greek historian and diplomat who visited India during the Maurya Empire, which was much earlier than the Vijayanagara period. He is known for his accounts of India in his book "Indica."

2. Yuan Chawng: Yuan Chawng, also known as Xuanzang, was a Chinese Buddhist monk who traveled to India during the Gupta Empire, again prior to the Vijayanagara period. He documented his journey in the book "Great Tang Records on the Western Regions."

3. Fa-hsien: Fa-hsien, also known as Faxian, was another Chinese Buddhist monk who visited India during the Gupta period, not the Vijayanagara period. He is famous for his travelogue called "Records of Buddhistic Kingdoms."

Therefore, option 4 - Nicolo Conti, is the correct answer. Nicolo Conti was an Italian merchant and traveler who visited India during the 15th century, which falls within the Vijayanagara period. His accounts provide valuable information about the Vijayanagara Empire and its culture.