F, Cl and Br are the elements each having seven valence electrons. Which of these (i) has the largest atomic radius, (ii) is most reactive? Justify your answer stating reason for each.

(i) The number of valence electrons determines the group of the element. F, Cl and Br have valence electrons 7 and belong to group 17. As we go down the group, new atomic shells are added. So, atomic size increases. Therefore, Br has the largest atomic radius as compared to Cl and F which has 3 and 2 shells respectively.

(ii) F is most reactive due to smaller size, high effective nuclear charge and high electro-negativity.