Which element among Chlorine and Argon has greater atomic mass. Why?

Dear student

Atomic mass of Cl is 35 μ
Atomic mass of Ar is 40 μ
So argon has greater atomic mass. 

Atomic mass = no. of protons + no. of neutrons
No. of protons and neutron in Ar is 18 and 22 respectively so atomic mass = 18 + 22 = 40
No. of protons and neutrons in Cl is 17 and 18 respectively so atomic mass = 17 + 18 = 35 

Regards