What element has a mass number of 40?
Sep 15, 2016
Mass number (A) of an element is equal to sum of protons and neutrons present in its nucleus.
So, in Argon
no. of electrons = 18
no. of protons = 18
no. of neutrons = 22
A = no. of neutrons + no. of protons
A = 22 + 18 = 40