Final answer:
Ethanol (-CH₃CH₂OH) is the most soluble of the given molecules in water due to its ability to form hydrogen bonds with water and having the shortest carbon chain among the options.
Step-by-step explanation:
The molecule most soluble in water among the provided options is -CH₃CH₂OH (ethanol). This is because ethanol has a hydroxyl group (-OH) capable of forming hydrogen bonds with water, making it highly water-soluble. In contrast, -C₂H₆ (ethane) is a nonpolar molecule with limited ability to interact with polar water molecules and therefore is the least soluble in water.
The other two molecules -CH₃CH₂CH₂CH₂OH and -CH₃(CH₂)₄NH₂ have hydroxyl and amino groups, respectively, and can also engage in hydrogen bonding with water, but their longer carbon chains make them less soluble than ethanol, which has the shortest carbon chain of the group.