this is because
first of all CCl4, it has symmetrical shape, so all of the polarity vectors will be cancel out so it will have zero dipole movement.
In CH3Cl the polarity vectors of 3 H atoms and Cl atoms add up and give it a large dipole moment...
In CH2Cl2 the polarity vectors of 2 H atoms add up to Cl atoms but vector of one Cl atom cancels half of the effect of other Cl atom and give it a smaller dipole moment compared to CH3Cl..
In CHCl3 the polarity vector of only one H atom adds up and 3 Cl atoms cancel each others effect and give it a much smaller dipole moment...
So order of relative dipole moments is:-
CCl4 < CHCl3 < CH2Cl2 < CH3Cl
Thanks a lot for replying...
No, it's wrong
Consider the case of ch2cl2
consider that both the cl atoms are at trans position which will an isomer of it then there you will get that the net dipole moment will be zero
But in the case of chcl3
you may take any isomer of it the net dipole moment will come out to be non zero and will have some of it