The radiation that is least dangerous as a threat to external portions of the body but is very dangerous if ingested or inhaled is:

• A. Beta
• B. Gamma
• C. Alpha
• D. Neutron

Answer: (C)

When thinking about radiation hazards, consider how far the radiation can travel in air and tissue, and what happens if it gets inside the body. Alpha particles are large and carry a strong charge, so they don’t travel far and are stopped by the outer layer of skin or even a sheet of paper. That makes them the least dangerous as an external exposure.

But if alpha emitters are inhaled or swallowed, they sit inside the body and deliver a lot of energy to nearby cells over a very short distance. That concentrated internal dose can cause significant damage to tissues and DNA, making alpha radiation extremely dangerous when ingested or inhaled.

Beta can penetrate a bit and gamma and neutrons penetrate more, which is why they pose greater external risks. The key idea is: alpha’s external danger is low, internal danger is high, so it best fits the description.