How does the number of subatomic particles change as the carbon isotope
decays?

Explanation:

C decays by a process called beta decay. During this process, an atom of 14C decays into an atom of 14N, during which one of the neutrons in the carbon atom becomes a proton. This increases the number of protons in the atom by one, creating a nitrogen atom rather than a carbon atom.

not clear

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.