Which of the following is an example of a refundable tax credit?

A refundable tax credit is a type of tax credit that allows taxpayers to receive a refund if the credit amount exceeds their tax liability. In the context of the given options, the Retirement Savings Contributions Credit, also known as the Saver's Credit, is indeed a refundable tax credit because it can result in a refund to taxpayers even if they owe no tax or their tax owed is reduced below zero.

The Child Tax Credit is a partially refundable credit, which means that while it may give back some amount as a refund, it does not fully fall into the category of a refundable credit like the Saver's Credit. The Educational Tax Credit can also vary in terms of refundability depending on its specific type (e.g., the American Opportunity Credit is partially refundable, while the Lifetime Learning Credit is not refundable). The Healthcare Premium Tax Credit generally reduces the amount of premium payments for health insurance but does not function as a refundable tax credit in the same comprehensive way the Saver's Credit does, being more related to health insurance affordability.

Thus, when identifying a refundable tax credit, the Retirement Savings Contributions Credit stands out as the correct choice.