## **Core Concept**
The question tests knowledge of the mechanism of action of various diuretics, specifically their effect on the Na+.K+.2Cl- symporter. This symporter is crucial in the thick ascending limb of the loop of Henle in the kidneys, where it facilitates the reabsorption of sodium, potassium, and chloride ions.

## **Why the Correct Answer is Right**
The correct answer, , is a type of diuretic known as a potassium-sparing diuretic. These diuretics primarily act on the collecting ducts of the kidneys. They either inhibit the epithelial sodium channel (ENaC) directly or inhibit the Na+-K+ ATPase pump indirectly, which leads to decreased sodium reabsorption and decreased potassium secretion. They do not act on the Na+.K+.2Cl- symporter.

## **Why Each Wrong Option is Incorrect**
* **Option A:** is a loop diuretic. Loop diuretics, such as furosemide, act by inhibiting the Na+.K+.2Cl- symporter in the thick ascending limb of the loop of Henle, which results in decreased reabsorption of sodium, chloride, and potassium.
* **Option B:** is also a loop diuretic. Like other loop diuretics, it inhibits the Na+.K+.2Cl- symporter.
* **Option D:** is another loop diuretic that works by inhibiting the Na+.K+.2Cl- symporter.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that loop diuretics (like , , and ) are the class of diuretics that primarily inhibit the Na+.K+.2Cl- symporter, and they are used in conditions requiring potent diuresis, such as acute heart failure or severe edema. In contrast, potassium-sparing diuretics (like ) are used for their effect on potassium levels and are often used in patients at risk of hypokalemia.

## **Correct Answer:** . Triamterene