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) Largest Atomic Radius:

• Answer: Bromine ($\text{Br}$) has the largest atomic radius among the three.
• Reason: $\text{F}$, $\text{Cl}$, and $\text{Br}$ belong to the same group (Group 17) in the periodic table. As we move down a group, the number of electron shells increases (Fluorine has 2 shells, Chlorine has 3, and Bromine has 4). This addition of new shells increases the distance between the outermost electrons and the nucleus, outweighing the increase in nuclear charge. Hence, the atomic radius increases down the group.

(ii) Most Reactive Element:

• Answer: Fluorine ($\text{F}$) is the most reactive element among the three.
• Reason: These elements are non-metals and react by gaining one electron to complete their stable octet. As we move down the group, the atomic size increases, and the distance between the nucleus and the outermost shell increases. Consequently, the nuclear attraction for an incoming electron decreases. Since Fluorine has the smallest atomic size, its nucleus exerts the strongest attractive force on an incoming electron, allowing it to gain an electron most readily. Thus, Fluorine is the most reactive.