Answer:
Atomic number is 18. Mass number is 38.
Explanation:
Atomic number is the number of protons in the nucleus of an atom. It is represented with letter Z. So, for the given question atomic number is 18.
Mass number is the total number of neutrons and protons in the nucleus of an atom. It is represented with letter A.
So, for the given problem:
A=Z+neutrons
A=18+20
A=38
