Which answer best describes an alpha particle?

a neutrino emitted during alpha decay

a positively charged nucleus with two protons and two neutrons

a particle that has no mass and no charge

an electron emitted by an unstable nucleus

A positively charged nucleus with two protons and two neutrons

Explanation:

Alpha particles consists of a positively charged nucleus with two protons and two neutrons. When alpha decay of a heavy element takes place, an alpha particle generally produced. It is represented as .

In an alpha decay, the mass number of an atom decreases by four and its atomic number decreases by 2.

For example, when the alpha decay of Uranium 238 happens it decays to thorium along with alpha particle.

Hence, the correct option is (B) " a positively charged nucleus with two protons and two neutrons  ".