Which type of radiation has the greatest penetrating ability?

Gamma rays have the greatest penetrating ability among the types of radiation listed. They are high-energy electromagnetic waves and do not have mass or charge, which allows them to penetrate materials much more deeply than alpha and beta particles.

Alpha particles, which comprise two protons and two neutrons, are relatively heavy and positively charged, making them easily absorbed by materials such as paper or even the outer layer of skin. Beta particles, being electrons or positrons, have more penetrating power than alpha particles but are still limited when it comes to penetrating thick materials.

In contrast, gamma rays can travel through several centimeters of lead or concrete before being significantly attenuated. This high penetration capability is a result of their electromagnetic nature, which allows them to pass through material without interacting as readily as charged particles do. Neutrons can also penetrate materials due to their neutral charge, but gamma rays generally have a higher penetration ability in most circumstances. Therefore, gamma rays are the most penetrating form of radiation, hence the correct choice.