The atomic numbers of the three elements X, Y and Z are 2, 6 and 10 respectively.
(i) Which two elements belong to the same group?
(ii) Which two elements belongs to the same period?
Give reasons for your choice.
(i) X and Z elements have atomic number 2 and 10. They have0 valency so they belong to the group of noble gas.
(iii) Y and Z have two valence electrons in their last shell so they belongs to the same period.