What is the main trade of India?

Mineral fuels, gems, precious metals are the main commodities in which India carries out its trade. You can read about Previous Years Economics Mains Questions for UPSC GS-3 in the given link.

Further readings:

1. UPSC Mains General Studies Paper-III Strategy, Syllabus & Structure
2. Topic-Wise GS 3 Questions for UPSC Mains