Which statement about alpha particles is true?

Which statement about alpha particles is true?

• A. They consist of two protons and two neutrons.
• B. They travel thousands of meters in air.
• C. They carry a negative charge.
• D. They have the smallest mass among common radiation.

Answer: (A)

Alpha particles are helium nuclei, consisting of two protons and two neutrons. This composition gives them a positive charge of +2e and a relatively large mass compared with other common radiation, which is why they are highly ionizing but have limited travel in air. They don’t travel thousands of meters in air; their range is only a few centimeters to tens of centimeters before being stopped by matter like a sheet of paper or skin. They are not negatively charged, and they are not the smallest-mass form of radiation—gamma rays have no mass, and beta particles have much smaller mass than an alpha particle. So the statement describing them as two protons and two neutrons accurately captures their fundamental nature.

Alpha particles are helium nuclei, consisting of two protons and two neutrons. This composition gives them a positive charge of +2e and a relatively large mass compared with other common radiation, which is why they are highly ionizing but have limited travel in air. They don’t travel thousands of meters in air; their range is only a few centimeters to tens of centimeters before being stopped by matter like a sheet of paper or skin. They are not negatively charged, and they are not the smallest-mass form of radiation—gamma rays have no mass, and beta particles have much smaller mass than an alpha particle. So the statement describing them as two protons and two neutrons accurately captures their fundamental nature.