Which of the following radiations can be stopped by a sheet of paper?

Alpha radiation is composed of helium nuclei, which consist of two protons and two neutrons. Due to their relatively large mass and positive charge, alpha particles have a strong interaction with matter and can be easily stopped by even a thin barrier, such as a sheet of paper. This characteristic makes alpha radiation less penetrating compared to other types of radiation.

In contrast, beta radiation consists of electrons or positrons, which are much smaller particles. They can penetrate further into materials than alpha particles and would require a denser barrier, like plastic or glass, for effective stopping. Gamma radiation and X-ray radiation are forms of electromagnetic radiation with very high energy and penetration power, requiring dense materials such as lead or several centimeters of concrete to significantly reduce their intensity. Therefore, a sheet of paper is not sufficient to stop either gamma or X-ray radiation.