**Core Concept**
Normal anion gap is a measure of the balance between cations and anions in the blood, calculated as the difference between sodium and the sum of chloride and bicarbonate concentrations (Na - (Cl + HCO3)). It reflects the unmeasured anions present in the body, such as lactate, ketones, and phosphate.

**Why the Correct Answer is Right**
The anion gap is increased in conditions where there is an accumulation of unmeasured anions, such as diabetic ketoacidosis (DKA), lactic acidosis, or renal failure. However, in metabolic alkalosis, the anion gap is typically normal because the excess hydrogen ions are compensated by a decrease in chloride ions, maintaining the anion gap within the normal range.

**Why Each Wrong Option is Incorrect**
* **Option A:** Not provided, cannot evaluate.
* **Option B:** Not provided, cannot evaluate.
* **Option C:** Not provided, cannot evaluate.
* **Option D:** Not provided, cannot evaluate.

**Clinical Pearl / High-Yield Fact**
In metabolic alkalosis, the anion gap remains normal because the body compensates for the excess hydrogen ions by decreasing chloride ion levels, often resulting in hypochloremic metabolic alkalosis.

**Correct Answer:** D.