**Core Concept**
The ability of a drug to be excreted unchanged in urine depends on its pharmacokinetic properties, particularly its lipid solubility and degree of ionization. Drugs that are highly ionized or have a high volume of distribution are more likely to be excreted through the kidneys in their unchanged form.

**Why the Correct Answer is Right**
The correct answer is a drug that is a weak acid or base, which remains ionized in the urine and is therefore not subject to extensive metabolism or reabsorption. This allows it to be excreted in its unchanged form. For example, a drug with a pKa value close to the pH of the urine (around 6-7) will be almost completely ionized, making it more water-soluble and increasing its excretion through the kidneys.

**Why Each Wrong Option is Incorrect**
* **Option A:** This drug is a highly lipid-soluble compound that is extensively metabolized in the liver before being excreted in the bile. Its high lipid solubility makes it unlikely to be excreted in its unchanged form.
* **Option B:** This drug is a weak base that is highly protein-bound in the plasma. Its high protein binding and limited ionization make it less likely to be excreted in its unchanged form.
* **Option C:** This drug is a highly ionized compound at physiological pH, but it is extensively reabsorbed in the renal tubules. Its reabsorption makes it less likely to be excreted in its unchanged form.

**Clinical Pearl / High-Yield Fact**
Drugs that are excreted unchanged in urine often have a narrow therapeutic index, and their dosing should be adjusted accordingly to avoid toxicity.

**Correct Answer:** C.