Which substance would you most likely need to cool to the lowest temperature before it condenses? ammonia (nh3), a polar covalent compound ethane (c2h6), a nonpolar covalent compound potassium bromide (kbr), an ionic compound

The substance that will take lowest temperature before it condenses is a polar covalent compound ethane(C2H6)

Explanation:

Nonpolar covalent compounds typically have the lowest boiling points.  Small alkanes/alkenes/alkynes have very low boiling points.  Their main inter molecular attraction is London dispersion forces, which are directly proportional to molecular mass, and thus are very weak in molecules such as methane, ethane/ethene, propane/propene, etc.  Thus, we can expect ethane to have the lowest boiling point.