Question

A normal carbon atom contains 6 protons 6 neutrons and 6 electrons.Then why should the atomic mass of corbon be 12 and not 18

Answer 1

because atomic mass no is protons+ neutrons

Answer 2

because electrons have negligible mass when compared with proton and neutron. also proton and neutron have nearly equal mass and each proton and neutron are taken as one unit of mass