Question

The least active halogen with hydrogen is
A. Chlorine
B. Fluorine
C. Iodine
D. Bromine

Answer 1

Hint: The more reactive halogen reacts with hydrogen highly. As we move from fluorine to iodine among halogens the size of the halogen atom increases and electronegativity decreases so, reactivity of halogen also decreases.

Complete Step by Step Answer:
As we move from fluorine to iodine among halogens the size of the halogens increases and electronegativity decreases. Among the halogens fluorine is most electronegative and iodine is least electronegative. Thus as the electronegativity difference between the hydrogen atom and halogens decreases the halogen becomes least active towards hydrogen. Thus among halogen hydrides hydrogen fluoride is the weakest and hydrogen iodide is the strongest halogen acid so, iodine is least active towards hydrogen.

Thus we can write that $HF$ is the weakest acid and most active towards hydrogen and hydrogen iodide is the strongest acid and least active towards hydrogen atoms.
So, iodine is least active towards hydrogen atoms.
Thus the correct option is C.

Note: Hydrogen reacts with fluorine to form hydrogen fluoride. It has a hydrogen bond. Hydrogen fluorine is the most acidic halogen acid.