Which of the following changes should improve water solubility? A. adding a methyl group B. adding a hydroxyl group C. adding a carboxyl group D. increasing the size of the drug E. adding a benzene ring

B. adding a hydroxyl group C. adding a carboxyl group

Explanation:

Solubility in water is due to the polar interactions or the hydrogen bonding.

Methyl group and benzene ring are both polar and hydrophobic in nature and thus will not improve water solubility.

Increasing size of drug will make more insoluble as more size of the solute is being added.

Adding hydroxyl or carboxyl group can improve water solubility as both the groups are highly hydrophilic and polar. These groups can form hydrogen bond with the water molecules and make drug more soluble in the water.