Which of the following diuretics is considered a potassium-sparing type?

Potassium-sparing diuretics are medications that help the body eliminate excess sodium and water while concurrently retaining potassium. Spironolactone is classified as a potassium-sparing diuretic because it works by antagonizing aldosterone in the distal convoluted tubule and collecting duct of the nephron. Aldosterone is a hormone that promotes the reabsorption of sodium and excretion of potassium; by blocking its action, spironolactone reduces sodium reabsorption and thus sodium and water excretion while conserving potassium.

The other diuretics listed, such as chlorothiazide and hydrochlorothiazide, belong to the thiazide category, which tends to promote potassium excretion along with sodium. Furosemide, a loop diuretic, functions similarly by inhibiting sodium reabsorption in the loop of Henle and also causes potassium loss. Therefore, spironolactone is distinguished as the only option that retains potassium, making it the correct choice in this context.