The correct option is A CH3Cl
Dipole is a physical quantity. Methane has zero dipole moment. Replacement of one H- atoms by Cl atom increases the dipole moment. The increase in dipole moment is because the bond dipole moment of C - H bond and that of C-Cl bond reinforce each other. Replacement of another H atom by Cl increases the bond angle due to lone pair - lone pair repulsion between Cl- atoms. This reduces the dipole moment and introduces the third Cl - atom. So when fourth Cl - atom is introduced the molecule (CCl4) again becomes symmetrical and dipole moment reduces to zero.So, CH3Cl has highest dipole moment.