Answer the following question given this paragraph: 

During a nuclear decay process that occurs by positron emission, a proton is converted into a neutron and a positron. The neutron remains in the nucleus, and the positron is expelled. Overall, the atomic number of the parent nucleus increases by one, and the mass number is unchanged. For example, carbon-11 emits a positron to become boron-11:.


Q: What happens to the mass number during a nuclear decay process by positron emission?

 Choices:

- it rises

- it decreases

- it increases

- remains unchanged

A:
remains unchanged
