Question

Which molecule contains both polar and nonpolar covalent bond?

• A. ${\mathrm{NH}}_4\mathrm{Br}$
• B. ${\mathrm{H}}_2{\mathrm{O}}_2$
• C. ${\mathrm{CH}}_4$
• D. $\mathrm{HF}$

Answer 1

The correct option is B

${\mathrm{H}}_2{\mathrm{O}}_2$

Explanation for correct option

(b) ${\mathrm{H}}_2{\mathrm{O}}_2$

• In this compound, oxygen is more electronegative than hydrogen.
• Hence, oxygen pulls the shared pair of electrons towards itself and because of this, oxygen has partial negative and hydrogen has partial positive charge in their two $\mathrm{O}-\mathrm{H}$ bonds.
• Whereas in $\mathrm{O}-\mathrm{O}$bond, the electronegativity is same and thus there is equal attraction of share pair of electrons on both sides.
• Hence, $\mathrm{O}-\mathrm{H}$ bond is polar and $\mathrm{O}-\mathrm{O}$ bond is non polar,
• Therefore, the correct option is (b) ${\mathrm{H}}_2{\mathrm{O}}_2$.

Explanation for incorrect options

(a) ${\mathrm{NH}}_4\mathrm{Br}$

• Bromine is more electronegative than hydrogen.
• This will result in partial negative charge on bromine since it will attract the shared pair of electrons towards itself.
• Hydrogen will have a partial positive charge.
• ${\mathrm{NH}}_4\mathrm{Br}$ will be a polar compound having dipole moment towards bromine.
• Hence, (a) ${\mathrm{NH}}_4\mathrm{Br}$ is the incorrect option.

(c) ${\mathrm{CH}}_4$

• In this molecule, $\mathrm{C}\mathrm{and}\mathrm{H}$ does not have much electronegativity difference.
• And hydrogen also evenly surrounds carbon cancelling all the poles against each other.
• Therefore, ${\mathrm{CH}}_4$ is a non- polar molecule.
• Hence, (c) ${\mathrm{CH}}_4$ is the incorrect option.

(d) $\mathrm{HF}$

• $\mathrm{H}\mathrm{and}\mathrm{F}$has unequal electronegativity.
• This results in non- uniform distribution of charge across them.
• Hence $\mathrm{HF}$ is a polar molecule.
• Therefore, (d) $\mathrm{HF}$ is the incorrect option.

Hence, the correct option is (b) ${\mathrm{H}}_2{\mathrm{O}}_2$.