Which of the following statements is/are true about trade?

Barter system is a part of trade

The correct answer is Option 2: Barter system is a part of trade

Option 1: Trade is a quaternary activity (Incorrect).  In the sector-wise classification of activities, Trade is classified as a Tertiary activity. Tertiary activities involve the provision of services (like retail, wholesale, and transport). Quaternary activities are "knowledge-based" services, such as research, information technology, and financial consultancy.

Option 2: Barter system is a part of trade (True) Trade is fundamentally the exchange of goods and services. While modern trade usually involves money as a medium of exchange, the Barter system—the direct exchange of goods for other goods without the use of money—is considered the earliest form of trade.

Option 3: Trade is only beneficial to the seller (Incorrect) While sellers aim to profit trade is mutually beneficial to both the buyer and the seller. 

NCERT: Trade means the voluntary exchange of goods and services. Two parties are required to trade. One person sells and the other purchases. In certain places, people barter their goods. For both the parties trade is mutually beneficial. Trade is a tertiary activity.