Which naturally-occurring radioactive particles are negatively charged

1. gamma radiation
2. neutrons
3. beta particles
4. alpha particle

Beta particles. Alpha, beta, and gamma are the first three letters of the Greek alphabet. After radioactivity was discovered, Ernest Rutherford showed that one type, entering a magnetic field, would curve in the direction a positive particle would curve. He called this alpha radiation and the resulting particles alpha particles. Another type would curve in the direction a negative particle would curve. He called this beta radiation and the particle a beta particle. Somewhat later a third type was found that did not curve in a magnetic field and was named gamma. The particle is simply a photon and is not charged. An alpha particle turns out to be 2 protons and 2 neutrons (a helium nucleus) and a beta particle turns out to be an electron. Neutrons are, of course, neutral.