Physics - Electrostatics Question with Solution | TestHub

Let us analyze the polarity of each given molecule:

Molecule (a) represents water ($H_{2}O$). It has a bent structure due to the presence of two lone pairs on the central oxygen atom. Because oxygen is more electronegative than hydrogen, the O-H bonds are polar. The vector sum of these bond dipoles is non-zero, resulting in a net dipole moment. Thus, $H_{2}O$ is a polar molecule.

Molecule (b) represents nitrogen ($N_2$). It is a homonuclear diatomic molecule. Since both atoms have the same electronegativity, the bond is nonpolar, making the molecule nonpolar.

Molecule (c) represents carbon dioxide ($C{O}_2$). It has a linear geometry. Although the C=O bonds are polar due to the electronegativity difference between carbon and oxygen, the two bond dipoles are equal in magnitude and opposite in direction. They cancel each other out, resulting in a net zero dipole moment. Thus, $C{O}_2$ is a nonpolar molecule.

Molecule (d) represents hydrogen ($H_2$). Like nitrogen, it is a homonuclear diatomic molecule with zero electronegativity difference, making it nonpolar.

Therefore, only molecule (a) is polar.

Answer: (a)