Na, Mg and Al are the elements of the same period of modern periodic table having one, two and three valence electrons respectively. Which of these elements (i) has the largest atomic radius, (ii) is least reactive ? Justify your answer stating reason for each case.

Explanation

(i) Na will have the largest atomic radius as atomic size goes on decreasing along a period from left to right. It is due to increase in nuclear charge (number of protons in nucleus) which pulls the electrons towards it, i.e., force of attraction between nucleus and valence electrons increases, therefore atomic size decreases.
(ii) Al is least reactive because reactivity of an clement depends upon the ability of its atoms to donate or accept electrons. Tendency to lose electrons along a period generally decrease with decrease in atomic size, i.e., the force of attraction between the valence electrons and the nucleus increases, therefore electrons cannot be removed easily.