Which uniform is not acceptable at events that require a coat and tie?

The Tropical Blue uniform is correct as the option that is not acceptable at events requiring a coat and tie. This type of uniform is designed for more casual, warm-weather conditions and does not incorporate the formalities associated with a coat and tie requirement.

In contrast, the Service Dress Blue and the Work Dress Uniform are structured and formal attire suitable for occasions that require a higher standard of dress, including events where a coat and tie are expected. The Operational Dress Uniform (ODU), while primarily intended for operational environments such as training and work settings, is also not in line with formal attire expectations.

Thus, when attending events that call for a coat and tie, the Tropical Blue uniform does not meet these criteria, making it the correct answer to the question.