Alpha particles are best described as:

• A. They travel far in air
• B. They are small and neutral
• C. They have no charge
• D. They are large mass; consist of 2 protons and 2 neutrons; carry a 2+ charge

Answer: (D)

Alpha particles are helium-4 nuclei: a relatively heavy, positively charged particle produced in certain radioactive decays. They consist of two protons and two neutrons, giving them a large mass for a single radiation particle and a 2+ electric charge from the two protons. This combination explains both their strong interaction with matter and their limited range in air, as they are easily stopped by a sheet of paper. So the description that best fits is: a large-mass particle made of two protons and two neutrons carrying a 2+ charge. The other statements mischaracterize alpha particles: they do not travel far in air, they are not neutral, and they do carry charge.