In an atom of element the sum of number of protons and neutrons is called nucleons. Nucleons = P + n
(protons + Neutrons)
For chlorine -37, no. of nucleons = n +p
n = (37 -17) +17; since, n = A +Z
No. of nucleons in = 37
Note: For an element number of nucleons is equal to its mass number.
Nucleons = Mass number