(i) Na has the largest atomic radius compared to Mg and Al. These elements belong to same third period
Reason: The atomic radius decreases when moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.(ii) Al is least reactiveReason: Al is smaller in size compared to Na and Mg so it has lesser tendency to lose electron due to high effective nuclear charge.