the electrons present in it has very less mass as compared to that of proton and hence it is not considered while calculation Atomic mass.
Mass of a Electron = (1/1849) times of proton
So The mass is protons and neutrons present in a atom is only considered as the mass of an atom
Atomic mass = mass of neutron+ mass of proton.
Sound is an energy
Sound propagate(means aage badna) in wave form
Wave form means aapne kabhi patther fenka hai taalaab main
After throwing stones you can see circular wave
When you want to walk you need a medium which is called land
In such a way to propagate sound they need air , water and land which is called medium
Islia moon per air no hone ki wajah se we are not be able to heard sound on moon