Which of the following is an example of a reserved power?

The designation of defense as an example of a reserved power is accurate because reserved powers in the context of the UK Parliament refer to areas of legislation that are retained by the central government and not devolved to the Scottish Parliament or other regional authorities. Defense falls squarely within this category as it is a matter that is managed at a national level, ensuring the security of the entire United Kingdom.

Education policy, in contrast, is a devolved power, allowing the Scottish Parliament to make decisions about the education system in Scotland. Similarly, transport regulation is also devolved, enabling local authorities and the Scottish Parliament to govern transportation matters specific to Scotland. Trade agreements, while often thought of in relation to national governance, can involve varied jurisdictions, but generally, they are linked more closely with reserved powers at a UK level rather than being an immediate local concern. Hence, defense unequivocally exemplifies a reserved power.