Answer:
X: 2,8 = Neon
Y: 2,8,7= Chlorine
Neon has an atomic number of 10. It is referred to as a noble gas and it’s a mono atomic element.
Chlorine has an atomic number of 17. It is referred to as an Halogen. Chlorine exists in nature as a diatomic molecule.
However the question is incomplete and will need more information.
