Final answer:
Aldosterone is the hormone that regulates the body's fluid and electrolyte balance by acting on the kidneys to retain sodium and water, thus preventing water loss.
Step-by-step explanation:
The compound among the choices that is a hormone helping the body maintain fluid balance is C. Aldosterone. Aldosterone plays a critical role in regulating the body's salt and water balance, which in turn affects blood pressure and blood volume. When the body has a low water content, decreased blood volume, or low blood pressure, aldosterone is released. It acts on the kidneys to conserve sodium and water, leading to an increase in fluid volume and helping maintain blood pressure. This action consequently prevents water loss and is part of the body's mechanisms to ensure homeostasis, the stable conditions necessary for the body's optimal functioning.