Among the three isomeric dichlorobenzenes , which has the highest boiling point and highest melting point ?

Explanation

Boiling point of o- dichlorobenzene is greater thanthe boiling point of m-and p-dichlorobenzenes due to its greater polar nature.
Boiling point order is : `O- > m- > P` dichlorobenzene.
Melting points of p-dichlorobenzene is greater than that of o- and m-dichlorobenzenes. It is due to symmetry of para-isomer of dichlorobenzene that fits in crystal lattice better as compared to o- and m-isomers. Melting points decrease in the order :
`p- > o- >m- `dichlorobenzene.