**Core Concept**
Fludrocortisone is a synthetic corticosteroid that exhibits predominantly mineralocorticoid activity, closely mimicking the effects of aldosterone. Its primary mechanism of action involves the regulation of electrolyte balance and water reabsorption in the kidneys.

**Why the Correct Answer is Right**
Fludrocortisone acts on the mineralocorticoid receptor in the collecting ducts of the kidneys, promoting sodium reabsorption and potassium excretion. This results in increased water reabsorption, leading to a rise in blood pressure and a decrease in serum potassium levels. The mineralocorticoid activity of fludrocortisone is responsible for its use in treating conditions such as Addison's disease and primary aldosteronism.

**Why Each Wrong Option is Incorrect**
**Option A:** Aldosterone is a naturally occurring mineralocorticoid, but it is not a synthetic steroid.
**Option B:** Dexamethasone is a synthetic corticosteroid with predominantly glucocorticoid activity, used for its anti-inflammatory and immunosuppressive effects.
**Option C:** Prednisolone is another synthetic corticosteroid with glucocorticoid activity, used for its anti-inflammatory and immunosuppressive effects.

**Clinical Pearl / High-Yield Fact**
Fludrocortisone is often used in conjunction with hydrocortisone in the treatment of Addison's disease, as it helps to replace the mineralocorticoid component of the hormone.

**Correct Answer: C. Fludrocortisone**