The halogens are Group 7. Group 7 consists of Flourine, Chlorine, Bromine, Iodine and Astatine.
Element Mass
Flourine 18.99
Chlorine. 35.5
Bromine. 79.9
Iodine. 126.9
Astatine 210
The answer is Flourine because it has a mass of less than 19 :) Hope this helps.
