Arrange the following in decreasing order of dipole moment
(1) m-Dichlorobenzene
(2) o-Dichlorobenzene (3) p-Dichlorobenzene

Options

A. `0 gt p gt m`
B. `p gt o gt m`
C. `m gt o gtp `
D. `0 gt m gtp`

Answer

D

Explanation

In p-dichlorobenzene, the two C-Cl diple (say x) are inclined at an angle of `60^(@).` Therefore, according to parallelogram law of forces, the resultant, dipole moment `(mu)`
`= sqrt (x ^(2) + x ^(2) + 2x xx cos 60^(@))`
` = sqrt (x ^(2) + x ^(2) + 2x ^(2) xx 1//2)`
` = sqrt ( 3x ^(2)) = sqrt 3x `
In m-dichlorobenzene, the two dipoles are inclined to each other at an angle of `120^(@),` thereofre, the resultant
`= sqrt (x ^(2) + x ^(2) 2x xx cos 120^(@))`
`= x ^(2) + x ^(2) + 2x ^(2) xx (-1 //2)`
`= sqrt ( x ^(2) =x`