**Core Concept**
Heat sterilization is a method used to eliminate microorganisms from surfaces and equipment. Oil and grease, being hydrophobic in nature, pose a challenge for traditional steam sterilization methods.

**Why the Correct Answer is Right**
The correct answer is a chemical sterilization method that utilizes a mixture of ethylene oxide and carbon dioxide to penetrate and inactivate microorganisms present in oil and grease. This method is effective because ethylene oxide is a potent biocide that can penetrate the hydrophobic environment of oil and grease, thereby eliminating microorganisms. The combination of ethylene oxide and carbon dioxide ensures that the sterilization process is efficient and effective.

**Why Each Wrong Option is Incorrect**
**Option A:** Autoclaving is not effective for sterilizing oil and grease because it relies on steam, which cannot penetrate the hydrophobic environment of these substances.
**Option B:** Dry heat sterilization is not suitable for oil and grease due to its slow and less effective penetration of the hydrophobic environment.
**Option C:** UV light sterilization is not effective for oil and grease as it relies on chemical reactions that do not occur in the absence of water.

**Clinical Pearl / High-Yield Fact**
Chemical sterilization methods, such as ethylene oxide gas, are essential for sterilizing equipment and surfaces that are hydrophobic or cannot be exposed to high temperatures or moisture.

**Correct Answer:** C. Ethylene oxide gas.