What happens during beta decay?

During beta decay, a fundamental transformation occurs within the nucleus of an atom. Specifically, one of the neutrons in the nucleus is converted into a proton, resulting in the emission of beta particles, which are electrons. This process increases the atomic number of the element by one, while the mass number remains unchanged, leading to the formation of a new element.

The emitted beta particle, which is essentially the electron, is what makes option B correct. This event is crucial in nuclear physics as it explains how unstable isotopes can transform into more stable forms through changes in their nuclear composition. This transformation helps to maintain the balance between protons and neutrons in the nucleus and is a hallmark of beta decay processes.

The other options reference different nuclear processes or particles that are not relevant to standard beta decay.