Question

Which bond is most polar?
A) \[Cl - F\]
B) \[Br - F\]
C) \[I - F\]
D) \[F - F\]

Answer 1

Hint: We need to know that halogens are nonmetals. At room temperature, fluorine and chlorine are gases and bromine is a liquid. Iodine and astatine are solids. Halogens are very reactive, the reactivity decreases from fluorine to astatine. Halogens do not exist in the elemental form in nature.

Complete answer:
We have to remember that the polarity of a bond is given by the difference in electronegativity between the two atoms that form said bond.
According to the Pauling scale, hydrogen has an electronegativity (EN) value of $2.20$. To get a polar covalent bond, the difference in EN between hydrogen and the other atom it bonds with must be greater than $0.5$ and smaller than \[1.7 - 1.8\]. Fluorine has highest electronegativity while iodine has least electronegativity among group 17 elements. Thus the electronegativity difference between fluorine and iodine is highest due to which they form the most polar bond. Molecules of all halogens are diatomic. What this means is that their molecules exist with two atoms each. Halogens have seven valence electrons because halogens have one electron missing; they form negative ions and are highly reactive. They can gain an electron by reacting with atoms of other elements. Fluorine is one of the most reactive elements in existence.

Option C is the correct answer.

Note:
We need to remember that the shared electrons of the covalent bond are held more tightly at the more electronegative element creating a partial negative charge, while the less electronegative element has a partial positive charge. The larger the difference in electronegativity between the two atoms; the more polar the bond.