Which of the following diuretics is considered potassium-sparing?

The correct choice is a diuretic that is classified as potassium-sparing, which means it helps the body retain potassium while promoting the excretion of sodium and water. Aldactone, known generically as spironolactone, fits this definition and works as an aldosterone antagonist. This action allows it to reduce the loss of potassium through urine, which is particularly beneficial in conditions where potassium levels need to be carefully managed, such as in patients with heart failure or certain types of renal disease.

In contrast, the other diuretics listed, such as chlorthalidone, furosemide, and hydrochlorothiazide, are not potassium-sparing. These diuretics typically promote the excretion of potassium along with sodium and water, which can lead to hypokalemia, or low potassium levels, in patients who are on these medications for extended periods or at high doses. Thus, Aldactone is favored in scenarios where potassium retention is desired.