Question

why chloromethane have more dipole moment than fluoromethane?

Answer 1

CH3Cl has larger dipole moment than CH3F because dipole moment is based on the product of distance and charge, and not just charge alone.

Fluorine is more electronegative than chlorine, but, the carbon-fluorine bond is also much shorter than the carbon-chlorine bond: 139 pm vs 178 pm. That's why the dipole moment of chloromethane is higher than the dipole moment of fluoromethane.