**Core Concept**
The question is testing the student's knowledge of the physical properties of radiation, specifically the penetrating power of different types of radiation. Penetrating power refers to the ability of radiation to pass through matter and is an important factor in radiation therapy and protection.

**Why the Correct Answer is Right**
The correct answer is **gamma rays**. Gamma rays have the highest penetrating power due to their short wavelength and high energy. They can travel long distances through the body and are often used in radiation therapy to treat deep-seated tumors. Gamma rays interact with matter primarily through the photoelectric effect and Compton scattering, which allows them to penetrate tissue more effectively than other forms of radiation.

**Why Each Wrong Option is Incorrect**
**Option A:** **X-rays** have a lower penetrating power than gamma rays due to their longer wavelength and lower energy. While they are still capable of penetrating tissue, they are more easily absorbed by denser materials such as bone and metal.
**Option B:** **Alpha particles** have a very low penetrating power due to their large mass and charge. They are easily absorbed by tissue and are not capable of penetrating the skin.
**Option C:** **Beta particles** have a moderate penetrating power, but are still less effective than gamma rays at penetrating tissue. They can travel a short distance through the body before being absorbed.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the penetrating power of radiation is an important consideration in radiation therapy, where the goal is to deliver a high dose of radiation to a tumor while minimizing damage to surrounding tissue. The choice of radiation type and energy is critical in achieving this balance.

**Correct Answer:** C. Gamma rays.