Final answer:
Carbohydrates, particularly glucose, mix with water and are a source of energy that can be stored and utilized by the body for biological functions.
Step-by-step explanation:
The molecule that can mix with water, serves as a source of energy, and is a storage area for energy in the body is carbohydrates. Carbohydrates, like glucose, are energy-rich organic compounds made up of carbon, hydrogen, and oxygen. When metabolized, glucose provides immediate fuel for cellular activities.
It is also stored in the body as glycogen, which can be later broken down for energy when needed. Lipids are another form of long-term energy storage but they do not mix with water as carbohydrates do. Therefore, the correct option is 'D carbohyd' (understood to mean carbohydrates).