Which of following has least difference  in melting point and boiling point ?A n-Pentane B 2-methylbutane C 2,2-dimethylpropane D 2-methylpropane

To determine which of the given compounds has the least difference in melting point and boiling point, we need to compare their structures and molecular weights.

A) n-Pentane: It is a straight-chain alkane with 5 carbon atoms. The molecular weight is 72.15 g/mol.

B) 2-methylbutane: It is a branched alkane with a methyl group attached to the second carbon atom. The molecular weight is 86.18 g/mol.

C) 2,2-dimethylpropane: It is a branched alkane with two methyl groups attached to the second carbon atom. The molecular weight is 58.12 g/mol.

D) 2-methylpropane: It is a branched alkane with a methyl group attached to the second carbon atom. The molecular weight is 58.12 g/mol.

Now, let's compare the melting and boiling points of these compounds. Generally, branching in a molecule decreases the boiling point and melting point compared to straight-chain compounds of similar molecular weight. This is because branching reduces the surface area available for intermolecular interactions, leading to weaker intermolecular forces.

Among the given compounds, 2,2-dimethylpropane (C) has the lowest molecular weight and the highest degree of branching. Therefore, it is expected to have the least difference in melting point and boiling point.

Hence, the compound with the least difference in melting point and boiling point is C) 2,2-dimethylpropane.