Which of the following particles is considered to be a beta particle?

A beta particle is a type of subatomic particle that is associated with beta decay, a process in which an unstable atomic nucleus transforms into a more stable one by emitting a beta particle. There are two types of beta particles: beta-minus (β-) and beta-plus (β+). The beta-minus particle is an electron, while the beta-plus particle is a positron (the antimatter counterpart of an electron).

In this context, the electron is the correct answer because it directly corresponds to the beta-minus decay, where a neutron is converted into a proton while emitting an electron (the beta particle) and an antineutrino. This process is fundamental in nuclear physics and helps to illustrate how isotopes can change their identities and achieve stability.

The other choices do not represent beta particles, as protons and neutrons are baryons that make up the atomic nucleus, while a helium nucleus consists of two protons and two neutrons, which is also not a beta particle. Therefore, the electron is identified as the beta particle due to its role in nuclear decay processes, solidifying its significance in particle physics.