Which is the best definition of voluntary exchange?

banks voluntarily provide a reasonable exchange rate for foreign currencies

the government provides laborers with money in exchange for their hard work

citizens choose to trade goods or services for something else of value

citizens voluntarily give up rights to the government for protection

I believe the answer is: citizens choose to trade goods or services for something else of value

Voluntary exchange could only happen if both parties involved are willingly committed to a certain type of transaction because they both genuinely believe that they will benefited from a the transaction. Examples of a voluntary exchange would be when a kid choose to spend their daily allowance to purchase his favourite candy.