Which ion has no ability to penetrate skin?

The ability of different types of radiation to penetrate biological tissues, including skin, varies significantly. Alpha particles are made up of two protons and two neutrons, essentially being helium nuclei. Due to their relatively large mass and positive charge, they possess a limited range and have difficulty penetrating matter.

When alpha particles encounter skin, they lose energy rapidly and are unable to penetrate even the outer layers of dead skin cells. This makes them comparatively harmless when exposure is limited to external contact. However, if alpha-emitting materials are ingested or inhaled, they can pose a significant internal hazard.

In contrast, beta particles, gamma rays, and X-rays have greater penetrating power. Beta particles are electrons that can pass through the skin to some extent. Gamma rays and X-rays are forms of high-energy electromagnetic radiation that can penetrate deeply into tissues, making them capable of causing more significant biological effects than alpha particles.

In summary, the correct choice emphasizes that alpha particles cannot penetrate skin, highlighting their limited interaction with biological tissues compared to other forms of radiation.