Which of the following is a type of radiation that poses an internal hazard that cannot penetrate clothing?

Alpha radiation is correct because it consists of heavy, positively charged particles (helium nuclei) that have a relatively large mass compared to other forms of radiation. This large size and charge mean that alpha particles have a very limited ability to penetrate materials. They can be stopped by just a few centimeters of air or even a sheet of paper, which is why they pose an internal hazard when ingested or inhaled but cannot penetrate clothing. This characteristic makes alpha radiation particularly dangerous when alpha-emitting materials enter the body but relatively safe in terms of external exposure.

In contrast, beta particles are lighter and can penetrate clothing and skin to some extent, while gamma radiation is highly penetrating and can pass through most materials, including human tissue. Delta radiation is less commonly referenced in this context, and the focus is typically on alpha, beta, and gamma for the types of ionizing radiation in terms of their hazards.