Which of the following molecules is non-polar in nature ?

The correct option is SbCl₅.

To determine which molecule is non-polar, we must examine the molecular geometry and the individual bond dipoles of each option:

1. SbCl₅ (Antimony pentachloride):
Antimony (Sb) is in Group 15 and has 5 valence electrons. In SbCl₅, Sb forms five single covalent bonds with five chlorine (Cl) atoms, leaving no lone pairs on the central antimony atom.
According to the VSEPR theory, a molecule with 5 bonding pairs and 0 lone pairs adopts a trigonal bipyramidal geometry.
In this highly symmetrical trigonal bipyramidal structure:
- The three equatorial Sb-Cl bonds lie in a plane at 120° angles to each other. Their dipole moments cancel each other out completely.
- The two axial Sb-Cl bonds point in opposite directions along a straight line (180° to each other), so their dipole moments also cancel each other out.
Because of this perfect spatial symmetry, the individual polar Sb-Cl bond dipoles cancel out completely, resulting in a net molecular dipole moment of zero ($\mu =0$). Therefore, SbCl₅ is non-polar.

2. POCl₃ (Phosphoryl chloride):
Phosphorus (P) is the central atom bonded to three chlorine atoms and one oxygen atom. Because oxygen is highly electronegative and the P-O bond is different from the P-Cl bonds, the tetrahedral structure is asymmetric. The bond dipoles do not cancel out, resulting in a net dipole moment ($\mu \ne 0$). Thus, POCl₃ is polar.

3. CH₂O (Formaldehyde):
Carbon is bonded to two hydrogen atoms and double-bonded to one oxygen atom in a trigonal planar geometry. Because oxygen is much more electronegative than carbon and hydrogen, there is a significant net dipole pointing toward the oxygen atom ($\mu \ne 0$). Thus, CH₂O is polar.

4. NO₂ (Nitrogen dioxide):
NO₂ is a bent molecule with a lone pair/unpaired electron on the central nitrogen atom. This asymmetric bent geometry means the polar N-O bonds do not cancel out, resulting in a net dipole moment ($\mu \ne 0$). Thus, NO₂ is polar.