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The melting points of compounds depend upon the following:

• Stronger intermolecular forces: These lead to higher melting points.
• The symmetry of the molecules: It also helps to determine the melting points of compounds. Compounds that have more symmetrical structures pack themselves very well into the crystalline lattices and have higher melting points.

a. The given compounds are pentane and butanamine. Between these two compounds, butanamine will have a higher melting point.

Pentane

Butanamine

Butanamine is a polar compound, and the intermolecular forces are very strong amongits molecules. It is also capable of forming hydrogen bonds, due to which the melting point becomes higher.

On the other hand, pentane has weak Van der Waals forces of attraction. Due to this, the melting point of pentane is low.

b. The given compounds are 2,2,3,3-tetramethyl butane and 3-methyl heptane. Between these two compounds, 2,2,3,3-tetramethyl butane will have a higher melting point.

2,2,3,3-tetramethyl butane

3-methyl heptane

Both these compounds have weak Van der Waals forces of attraction. However, the molecules of 2,2,3,3-tetramethyl butane are more spherical in nature due to the presence of branching in the molecule. As a result, the molecules can pack more closely, and the melting point increases.