Which of the following is an example of a public sector trade union?

Teachers are indeed an example of a public sector trade union because they typically work for government-run institutions such as public schools and colleges. Public sector trade unions represent employees who work in government and public services, advocating for their rights, negotiating wages, and ensuring fair working conditions.

In contrast, the other groups listed—factory workers, retail employees, and construction workers—primarily operate within the private sector, which involves different organizations and industries. Each of these groups may have their own trade unions, but they do not belong to the public sector in the way that teachers do. Therefore, focusing on the public context of their employment allows for a clear identification of teachers as part of a public sector trade union.