Question

Statement-I: The boiling points of alkyl chlorides are higher than hydrocarbons of comparable mass. Statement-II: The melting point order of dihalobenzenes is:

Answer 1

Statement-I is true. Statement-II is false.

Answer 2

Statement-I: Alkyl chlorides (haloalkanes) are polar molecules due to the electronegativity difference between carbon and chlorine atoms, leading to dipole-dipole interactions. Hydrocarbons are nonpolar and exhibit London dispersion forces. Since alkyl chlorides have stronger intermolecular forces, they have higher boiling points. Hence, Statement I is True.

Statement-II: Melting points are determined by the efficiency of molecular packing in the crystal lattice. Para-isomers are highly symmetrical, allowing efficient packing and stronger intermolecular forces, leading to higher melting points. Ortho and meta isomers are less symmetrical and pack less efficiently.

The melting points are:

• Ortho-dichlorobenzene: -17 °C
• Meta-dichlorobenzene: -24 °C
• Para-dichlorobenzene: 53 °C

The correct order is: Meta-dichlorobenzene < Ortho-dichlorobenzene < Para-dichlorobenzene.

The statement (ortho < meta < para) is incorrect. Hence, Statement II is False.