Final answer:
Ensuring that the bottom sheet is free of wrinkles is an essential action when a nurse makes an unoccupied bed, as it helps prevent patient discomfort and skin issues.
Step-by-step explanation:
When a nurse must make an unoccupied bed, certain actions are essential to ensure patient safety and comfort once the bed will be used. Among the provided options, ensuring that the bottom sheet is free of wrinkles is an essential nursing action. This is important because wrinkles in the sheet can cause discomfort and may lead to the development of pressure sores or skin irritation for patients. Other actions, such as placing a pull sheet on top of the draw sheet, may be part of the bed-making process but are not as critical when making an unoccupied bed.