A stock exchange is a market that

A stock exchange is a formal, regulated marketplace where securities - such as shares (stocks), bonds, debentures, and government securities - are bought and sold. It provides a platform for companies to raise capital by issuing shares to the public and for investors to trade those shares among themselves.

The correct answer is that a stock exchange deals with the purchase and sale of securities. Key functions of a stock exchange include:

• Providing a secondary market where existing securities can be traded, giving investors liquidity.
• Facilitating price discovery through the forces of supply and demand.
• Protecting investors through regulations, listing requirements, and transparency rules.
• Mobilising savings and channelling them into productive investment.

A stock exchange does not deal with the exchange of physical commodities - that is the function of a commodity exchange or commodity market. The other two options are nonsensical distractors that do not describe any recognised financial market.

Examples of stock exchanges include the Nigerian Stock Exchange (now Nigerian Exchange Group), the London Stock Exchange, and the New York Stock Exchange.