Nucleus: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Nucleus. Understanding the underlying formula is key to arriving at the correct answer below:

In $\beta^+$ (positron) decay, a proton is converted into a neutron, releasing a positron ($e^+$ or $\beta^+$) and an electron neutrino ($\nu$) to conserve lepton number. Hence, particle X is a neutrino.