Which of the following statements is true about alpha particles?

Alpha particles are indeed the most massive of the common types of radiation, which include alpha, beta, and gamma rays. Being composed of two protons and two neutrons, they have a relatively large mass compared to beta particles and gamma rays. This increased mass is accompanied by a lower velocity, making alpha particles the slowest moving among these radiation types.

In terms of penetration, alpha particles have a very limited range. They can be stopped by a piece of paper or even the outer layer of human skin, which means they are the least penetrating of all the radiation types. Their inability to penetrate thick materials effectively makes them relatively less hazardous when outside the body, though they can pose significant risks if alpha-emitting materials are ingested or inhaled.

This understanding underlines the characteristics of alpha particles, solidifying why the identified answer aligns accurately with their fundamental properties.