Step 1: Understand the meaning of "barter".
"Barter" means the act of trading goods or services between two people or groups without using money.
Step 2: Analyze the options.
SEIZE: To forcibly take something — not related to mutual trade.
REMOVE: To take something away — unrelated to trading.
STEAL: Taking without permission — completely opposite to legal exchange.
EXCHANGE: Giving one thing and receiving another in return — this matches perfectly with "barter".
Thus, the correct synonym is EXCHANGE.