Question

Is it true that atomic mass is double the atomic number..because the atomic num. of helium is 2 & it mass is 4..

Answer 1

the great extent it is true but it is not true for all elements

Answer 2

No....It happens in most of the cases but actually,

Atomic mass= No. of protons + No. of neutrons...

You're right atomic number of Helium is 2 and its atomic mass is 4......But you can also see that the atomic number of sodium is 11 and its atomic mass is 23...so here, this illusion fails but not that formula...