**Core Concept**
Spontaneous non-enzymatic degradation in plasma refers to the chemical breakdown of a drug due to its inherent chemical properties, such as pH sensitivity, light sensitivity, or oxidation, rather than through the action of enzymes.

**Why the Correct Answer is Right**
The correct answer is likely a drug that is susceptible to hydrolysis, oxidation, or other non-enzymatic chemical reactions that occur in the plasma environment. This type of degradation can be influenced by factors such as pH, temperature, and light exposure. For example, some antibiotics, such as penicillins, are susceptible to hydrolysis by plasma esterases, but this is not the correct answer. Instead, the correct answer is likely a drug that undergoes spontaneous degradation due to its chemical properties.

**Why Each Wrong Option is Incorrect**
**Option A:** This option may be incorrect because it could refer to a drug that is primarily metabolized by enzymes, such as the cytochrome P450 system, rather than undergoing non-enzymatic degradation.
**Option B:** This option may be incorrect because it could refer to a drug that is inactivated by enzyme-mediated reactions, such as glucuronidation or acetylation, rather than spontaneous degradation.
**Option C:** This option may be incorrect because it could refer to a drug that is primarily excreted unchanged in the urine, rather than undergoing non-enzymatic degradation in the plasma.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the stability of a drug in plasma can be influenced by various factors, including pH, temperature, and light exposure. This knowledge can help clinicians predict potential drug degradation and optimize dosing regimens accordingly.

**Correct Answer:** D.