(a) The elements with completely filled shells are noble gas elements and they belong to group 18. Since the element has two shells, it must be present in second period and it is neon (Ne) with electronic configuration 2, 8.

Periodic Table, let us identify the group and period to which these elements belong Since the metallic character increases down a group and decreases along a period, the obvious choice is between two elements. These are Be (beryllium) present in group 2 and Ga (gallium) present in group 13.

Period - 1 - 3 - 4

Group 2 Be,  -,  -

Group 13  -, - , Ga 

Group 14 - , - , Ge

Group 15 - , - , As

Group 16 - , - , Se

(b) The electronic configuration suggests that the element belongs to third period and second group. It is, therefore, magnesium (Mg).

(c) The element with three shells is present in third period. Since it has four electrons in the valence shell, it must belong to group 14 and is silicon (Si) with electronic configuration 2, 8, 4.

(d) The element with two shells is expected to be present in the second period. With three electrons in the valence shell, it must belong to group 13 and is boron (B) with electronic configuration 2, 3.

(e) The element has only two shells. The first shell can have a maximum of two electrons. The second shell has four electrons which is twice the number of electrons present in the first shell. Therefore, the electronic configuration of element is 2, 4. It is carbon with atomic number (Z) equal to 6.