Question

P-dichlorobenzene has higher melting point than its ortho and meta isomers

Answer 1

it's Because The p- isomers being more symmetrical and fits closely in the crystal lattice and thus has stronger inter-molecular forces of attraction than o- and m- isomers .
As during melting or dissolution , the crystal lattice breaks , therefore a large amount of energy is needed to melt or dissolve the p - isomer than the corresponding o-and m-isomers .