Answer:
D. [tex]^{39}_{18} Ar[/tex]
Explanation:
The given nuclear equation is the beta decay of chorine in which an electron, known as a beta particle, is given off from within the nucleus due to the breakdown of a neutron within the nucleus into a proton and a beta particle, such that the atomic number is increased by 1 from 17 to 18, which is the atomic number or argon, Ar, as follows;
[tex]^{39}_{17}Cl \ \rightarrow \ ^0_{-1} e + \ ^{39}_{18} Ar[/tex]
