Answer:
Iodine (I)
Step-by-step explanation:
The atomic mass of Arsenic (As) is 74.92 amu. Also, we know that Halogen Group consists of following elements.
Fluorine, Chlorine, Bromine, Iodine, Astatine and Tennessine
And in given four options only Chlorine and Iodine belongs to halogen family. And we know that the atomic mass of chlorine is 35.45 amu which is less than that of Arsenic, therefore Iodine with atomic mass of 126.90 amu is the correct answer.