In atomic mass units $($u$),$

Question $4$ options:

the mass of an electron, proton, or neutron is approximately $1$ u$.$

the mass of a proton or neutron is approximately $1$ u$,$ and the mass of an electron is approximately $0$ u$.$

the mass of an atom is approximately equal to the number of electrons and neutrons in the nucleus of the atom.

the mass of a carbon$-12$ atom is exactly $6$ u$.$

the mass of an$17$ O atom is approximately $16$ u$.$