Which of the following is polar molecule?

The correct option is CHCl₃.

Understanding Molecular Polarity:
A molecule is polar if it has a non-zero net dipole moment:

$$\overrightarrow{\mu }\ne 0$$

The net dipole moment is the vector sum of all individual bond dipole moments. If a molecule has a highly symmetric shape and all surrounding atoms are identical, the individual dipoles cancel each other out, making the molecule non-polar. However, if the molecule is asymmetric or contains different types of terminal atoms, the dipoles do not cancel, resulting in a polar molecule.

Step-by-Step Analysis of the Options:

1. CH₂ = CH₂ (Ethene):
As indicated in the provided image, ethene is a symmetric, planar molecule. The individual dipoles of the C−H bonds cancel each other out due to the center of symmetry. Therefore, it is non-polar.

2. CCl₄ (Carbon tetrachloride) and CH₄ (Methane):
The provided diagram highlights that both of these molecules have "spherical symmetry."
Both molecules adopt a perfect tetrahedral geometry (sp³ hybridized carbon). Because all four surrounding bonds (C−Cl in CCl₄ and C−H in CH₄) are identical and symmetrically arranged, their individual bond dipoles cancel out completely:

$${\mu }_{\text{net}}=0$$

Thus, both CCl₄ and CH₄ are non-polar.

3. CHCl₃ (Chloroform):
In CHCl₃, the central carbon is bonded to three highly electronegative chlorine atoms and one hydrogen atom.
As illustrated in the dipole vector diagram in the image:
• The C−H bond dipole points towards the carbon atom (since carbon is slightly more electronegative than hydrogen).
• The three C−Cl bond dipoles point away from the carbon atom towards the highly electronegative chlorine atoms.
Because the terminal atoms are not identical, the symmetry is broken. The dipoles reinforce each other rather than canceling out, resulting in a net dipole moment pointing downwards towards the chlorine atoms:

$${\mu }_{\text{net}}\ne 0$$

Therefore, CHCl₃ is a polar molecule.