Final answer:
The main intermolecular force in pentane is London dispersion force, which is due to its nonpolar nature and the physical contact between the elongated shapes of its molecules.
Step-by-step explanation:
The predominant intermolecular force (IMF) in pentane is the London dispersion force. Pentane is a nonpolar molecule and does not exhibit hydrogen bonding or significant dipole-dipole interactions, which are commonly found in more polar molecules. Therefore, dispersion forces are the main IMFs responsible for the physical properties of liquids such as boiling point, melting point, and vapor pressures in pentane.
The presence and strength of these dispersion forces are directly related to the molecular mass and shape of the molecule; in the case of pentane, the elongated shape of its molecules allows for increased surface contact and stronger dispersion forces compared to its branched isomers, isopentane and neopentane.