**Core Concept**
The kidneys play a crucial role in maintaining electrolyte balance and waste removal from the body. Normally, the kidneys filter waste products, excess ions, and water from the blood and excrete them in the urine. However, certain substances are not excreted in urine due to their physicochemical properties or the presence of specific transport mechanisms.

**Why the Correct Answer is Right**
Substances with a high molecular weight, those that are highly lipid-soluble, or those that are actively reabsorbed in the renal tubules are not normally excreted in the urine. Water-soluble substances with a low molecular weight, on the other hand, are readily excreted in the urine. This is due to the presence of specific transport mechanisms, such as the sodium-potassium pump, which helps maintain electrolyte balance.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is a water-soluble substance with a low molecular weight, making it readily excreted in the urine.
**Option B:** Incorrect because it is a water-soluble substance with a low molecular weight, making it readily excreted in the urine.
**Option D:** Incorrect because it is a water-soluble substance with a low molecular weight, making it readily excreted in the urine.

**Clinical Pearl / High-Yield Fact**
Substances that are not normally excreted in the urine can accumulate to toxic levels if kidney function is impaired. This highlights the importance of maintaining proper kidney function to prevent electrolyte imbalances and waste accumulation.

**Correct Answer:** C.