The formula of an ion of an element A is A²⁺. Element A probably belongs to which group?

State the group and period of the element having three shells with three electrons in the valence shell.

Arrange the following in order of :

(i) increasing radii.

(a) Cl^-, Cl
(b) Mg²⁺, Mg, Mg⁺
(c) N, O, P

(ii) increasing ionisation energy.

(a) P, Na, Cl
(b) F, O, Ne
(c) Ne, He, Ar

Explain your choice.

Atomic numbers of elements A, B, C, D, E, F, are 8, 7, 11, 12, 13 and 9 respectively. State the type of ions they form.