**Core Concept**
Oral rehydration solution (ORS) is a specially designed fluid used to treat dehydration caused by diarrhea, particularly in children. It contains essential electrolytes, such as sodium, potassium, and chloride, which help replace lost fluids and maintain proper bodily functions.

**Why the Correct Answer is Right**
ORS has been employed in the treatment of other conditions beyond diarrhea, such as cholera, typhoid fever, and even in the management of hyperemesis gravidarum, a condition characterized by severe nausea and vomiting during pregnancy. The key to ORS's effectiveness lies in its ability to replenish fluids and electrolytes, which is crucial in conditions where there is excessive loss of fluids and electrolytes through vomiting or diarrhea.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as there is no widely recognized use of ORS in the treatment of malaria.
**Option B:** This option is incorrect as there is no established role for ORS in the management of hypertension.
**Option C:** This option is incorrect as there is no documented use of ORS in the treatment of chronic kidney disease.

**Clinical Pearl / High-Yield Fact**
It's worth noting that ORS can be used as a carrier for certain medications, such as azithromycin, to improve compliance and absorption in patients with gastrointestinal infections.

**Correct Answer:** C.