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.

(i) In order of increasing radii:

(a) Cl < Cl^-.
Reason — Anion is greater in size than its parent atom.

(b) Mg²⁺ < Mg⁺ < Mg.
Reason — Cation is smaller in size than its parent atom.

(c) O < N < P.
Reason — Between Oxygen (O) and Nitrogen (N), atomic size of Nitrogen (N) is more as it is to the left of Oxygen (O) in period 2. Between Nitrogen (N) and Phosphorus (P), Phosphorus (P) has larger atomic size as it comes after Nitrogen (N) in group 5A.

(ii) In order of increasing ionisation energy:

(a) Na < P < Cl
Reason — Ionisation energy increases when moving across a period from left to right.

(b) O < F < Ne
Reason — Ionisation energy increases when moving across a period from left to right.

(c) Ar < Ne < He
Reason — Ionisation energy decreases when moving down the group.