Final answer:
Molecular weight is the property that affects the solubility of alcohols in water, with heavier alcohols having longer carbon chains being less soluble due to increased hydrophobic character.
Step-by-step explanation:
The student asked which property of alcohols makes them insoluble in water. The options provided were A. Hydrogen bonding B. Presence of hydroxyl group C. Molecular weight D. Ionization. The property that directly affects the solubility of alcohols in water is C. Molecular weight. While it is true that alcohols can engage in hydrogen bonding due to the presence of the hydroxyl group, these properties generally contribute to their ability to dissolve in water, making them more hydrophilic. However, as the molecular weight of the alcohol increases, or more specifically, as the length of the carbon chain in the alcohol increases, its solubility in water decreases. This phenomenon occurs because longer carbon chains increase the hydrophobic character of the molecule, overpowering the hydrophilic effect of the hydroxyl group. Therefore, while lighter alcohols with shorter chains, such as methanol, ethanol, and propanol, are completely soluble in water, heavier alcohols, like 1-decanol, are essentially insoluble in water due to their larger molecular weight and the increased length of the carbon chain.