**Core Concept**
Radium is a radioactive element that undergoes alpha, beta, and gamma decay, emitting various types of ionizing radiation. This process involves the transformation of radium's unstable nucleus, resulting in the emission of radiation.

**Why the Correct Answer is Right**
Radium primarily emits alpha particles, which are high-energy helium nuclei that can cause significant ionization in tissues. This is due to the fact that radium's nucleus undergoes alpha decay, where a helium nucleus is ejected from the nucleus, resulting in a more stable configuration. The emission of alpha particles is the primary mode of radiation for radium.

**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable, as we don't have enough information about other options yet.
**Option B:** Incorrect, as radium does not primarily emit beta particles. While it can undergo beta decay in certain circumstances, alpha decay is its primary mode of radiation.
**Option C:** Incorrect, as radium does not primarily emit gamma radiation. Gamma radiation is a secondary product of radium's decay, but it is not its primary mode of radiation.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that radium's alpha emissions can be stopped by a sheet of paper or a few centimeters of air, making it a relatively safe element in terms of external radiation exposure.

**Correct Answer: C. Gamma radiation**