Answer:

Atomic number z=35

Mass number=80

No. of proton p=35

No. of neutron n=80−35=45

No. of electron e=35

Explanation:
Mg:
electron=12

proton=12
Mass no =24
He:
electron=2
proton=2
Mass no=4
Ne:
electron=10
proton=10
Mass no =20
Silicon:
electron=14
proton=14
Mass no=28
Nitrogen:
electron=7
proton=7
Mass no=14