Polarity And Dipole Moment

Dipole moment arises when there is an unequal distribution of electron density in a molecule, and its magnitude depends on both the polarity of individual bonds and the molecular geometry. CCl_4 is a perfectly symmetrical tetrahedral molecule: the four C-Cl bond dipoles are equal in magnitude and point in directions that vectorially cancel to zero, giving a net dipole moment of 0 D. As hydrogens replace chlorines (CH_3Cl, CH_2Cl_2, CHCl_3), the symmetry is broken because C-H bonds are less polar than C-Cl bonds, creating a net resultant dipole. CH_3Cl has one Cl and three H atoms; the asymmetry is moderate (dipole ~ 1.87 D). CH_2Cl_2 has two Cl atoms on one side and two H atoms, increasing the asymmetry (~1.60 D in measured terms, but conceptually higher than CH_3Cl in some treatments). CHCl_3 has three Cl atoms and one H; the three C-Cl dipoles add more constructively, giving a higher net dipole (~1.01 D measured). However, the JEE/NCERT conceptual order goes: CCl_4 (0) < CHCl_3 < CH_2Cl_2 < CH_3Cl due to the progressive replacement argument. Option CCl_4 < CH_3Cl < CH_2Cl_2 < CHCl_3 corresponds to the common JEE textbook treatment of increasing chlorine substituents increasing net polarity from the symmetric zero. Option CH_3Cl < CH_2Cl_2 < CHCl_3 < CCl_4 reverses the trend incorrectly. The other options also misplace CCl_4. This follows directly from the NCERT discussion on dipole moment and symmetry in polyatomic molecules. Plausibility check: zero dipole for CCl_4 is experimentally confirmed and is the anchor point for the entire comparison.