Which among the following elements has the largest atomic radii? [NCERT Exemplar](a) Na(b) Mg(c) K(d) Ca

(c) Atomic radius increases on moving down in a group. Na and K are in the same group and K is below Na, so K will have higher atomic radius, i.e. K > Na. In a period on moving left to right, atomic radius decreases. Since, K and Ca are in the same period and K is in 1st group and Ca is in 2nd group, so atomic radius of K will be more than Ca, i.e. K > Ca. Also Na and Mg are in the same period, but Na belongs to 1st group and Mg belongs to 2nd group, so atomic radius of Na is more than Mg, i.e. Na > Mg. Thus, if we take all these together we get K > Na >Mg and K > Ca > Mg. Hence, we can say that the atomic radius of K is largest.