Na, Mg and AI 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.

(i) Na has the largest atomic radius because on moving from left to right in the periodic table, the atomic radius decreases due to increase in positive charge on the nucleus which pulls the outermost electrons in more close to the nucleus and the size of atom decreases.

(ii) AI is least reactive because on moving from left to right in the periodic table the nuclear charge increases and the valance electrons are pulled in more close to the nucleus. Therefore, the tendency to lose electrons decreases and hence reactivity decreases.