Alpha particles can be stopped by which of the following?

Alpha particles are relatively heavy and positively charged particles emitted during certain types of radioactive decay. Their large mass and charge mean they interact strongly with matter, leading them to lose energy quickly as they collide with atoms in a material.

When we consider the options given, the correct answer states that alpha particles can be stopped by a few particles of air and a sheet of paper. This is accurate because alpha particles are significantly attenuated by even a small amount of matter. In fact, they can typically be stopped by just a few centimeters of air or a thin sheet of paper. The dense nature of alpha particles allows them to be absorbed and their energy dissipated with minimal material.

Conversely, the other options involve materials that do not effectively stop alpha particles in such small quantities. Several meters of air, while it can attenuate alpha particles, would require a far greater distance than just a few particles to achieve significant stopping. Plastic sheets and wood may offer more substantial barriers but still imply a thickness or amount that exceeds what is necessary for the alpha particles to be fully absorbed. Thus, the minimal interaction required to stop alpha particles highlights their unique qualities compared to other forms of radiation.