In beta-plus decay (also known as positron emission), a proton in the nucleus is transformed into a neutron, which results in the emission of a positron and a neutrino.
As a result:
- The mass number remains the same (since the total number of nucleons, protons + neutrons, does not change).
- The atomic number decreases by one (since one proton is transformed into a neutron).
Therefore, the correct response is:
The mass number remains the same, and the atomic number decreases by one.