**Core Concept**
The question is testing the sodium-retaining potential of various corticosteroids, which is a key aspect of their mineralocorticoid activity. Corticosteroids with high mineralocorticoid activity promote sodium retention, water retention, and potassium excretion, leading to increased blood pressure and fluid volume expansion.

**Why the Correct Answer is Right**
The correct answer is **Betamethasone**, which has a relatively high sodium-retaining potential compared to other corticosteroids. This is due to its moderate to high mineralocorticoid activity, which is reflected in its glucocorticoid-to-mineralocorticoid potency ratio. Betamethasone's mineralocorticoid activity is comparable to that of fludrocortisone, a potent mineralocorticoid.

**Why Each Wrong Option is Incorrect**
**Option A:** **Prednisone** has a relatively low sodium-retaining potential due to its weak mineralocorticoid activity, making it a less potent mineralocorticoid compared to betamethasone.

**Option B:** **Prednisolone** also has a low sodium-retaining potential due to its weak mineralocorticoid activity, similar to prednisone.

**Option C:** **Dexamethasone** has an even lower sodium-retaining potential than prednisone and prednisolone, as it has very weak mineralocorticoid activity.

**Clinical Pearl / High-Yield Fact**
When selecting a corticosteroid for patients with conditions like adrenal insufficiency or hypotension, it's essential to choose a corticosteroid with minimal mineralocorticoid activity, such as dexamethasone or methylprednisolone, to avoid excessive sodium and water retention.

**Correct Answer:** D. Betamethasone.