In alpha decay, which particle is emitted from the nucleus of an unstable atom?

• A. A beta particle (an electron)
• B. A neutron
• C. A helium-4 nucleus (2 protons and 2 neutrons)
• D. A positron

Answer: (C)

Verified step by step guidance

1. Understand that alpha decay is a type of radioactive decay where an unstable nucleus emits a specific particle to become more stable.
2. Recall that the particle emitted in alpha decay is called an alpha particle, which is essentially a helium-4 nucleus composed of 2 protons and 2 neutrons.
3. Recognize that this emission reduces the atomic number of the original nucleus by 2 and the mass number by 4, leading to the formation of a new element.
4. Differentiate alpha particles from other particles such as beta particles (electrons), neutrons, and positrons, which are involved in other types of radioactive decay processes.
5. Conclude that the correct particle emitted in alpha decay is the helium-4 nucleus (2 protons and 2 neutrons), also known as the alpha particle.