Final answer:
Alpha radiation is most dangerous when contained inside an aluminum box because, if ingested or inhaled, it can deposit all its energy into internal tissues causing significant damage.
Step-by-step explanation:
Among the types of radiation listed, alpha radiation (A) is most likely to be dangerous if the source is kept inside an aluminum box. While gamma rays and X-rays have high penetrating power, an aluminum box can effectively block alpha particles if the source is external. However, if alpha-emitting material is ingested or inhaled, it becomes very dangerous because alpha particles can deposit all of their energy into nearby tissues, causing significant damage. Beta radiation (B) can penetrate materials to some extent but is generally stopped by a thin layer of metal, like aluminum. Gamma radiation (C) and X-ray radiation (D) are highly penetrating and can pass through thicker layers but would require denser materials such as lead for effective shielding.