Which one of the following has higher vapour pressure?

Explanation

This is the option marked correct in the official UHS answer key. Isopentane is a branched non polar hydrocarbon whose only intermolecular attractions are weak dispersion forces, and branching reduces the contact area further, so it evaporates readily. Note that acetaldehyde, boiling at about 21 degrees Celsius, is in fact the more volatile of the two in standard data, so this is a question where the official key is worth knowing alongside the underlying principle that weak intermolecular forces mean high vapour pressure.