Question

Which of the following Group 17 elements is the least reactive?

Answer 1

The given question is incomplete. The complete question is :

Which of the following Group 17 elements is the least reactive

a) Flourine

b) Chlorine

c) Astatine

d) Iodine

Answer: c) Astatine

Explanation:

Halogen is the name given to Group 17 family with general electronic configuration of $ns^2np^5$ which have 7 valence electrons and thus easily gain one electron to attain stable configuration.

As we move down the group from flourine to chlorine to bromine to iodine to astatine , the valence shell moves farther from nucleus and thus tendency to accept the electron decreases and thus reactivity also decreases.

Thus Astatine is the least reactive of all.