Final answer:
At a pH above the pKa of the side chain of phenylalanine, the phenolic group is deprotonated and carries a negative charge, so the correct answer is (d) Deprotonated and negatively charged.
Step-by-step explanation:
At a pH above its pKa(side chain), the phenolic group of phenylalanine is deprotonated and negatively charged. The pKa of a molecule is the pH at which half of the molecules of that species are deprotonated. When the pH is higher than the pKa, there are more hydroxide ions (OH-) available in the solution, favoring deprotonation. As a result, the phenolic group of phenylalanine, which can release a proton from its hydroxyl group, will be in a deprotonated state. Since losing a proton results in a negative charge, the correct answer is (d) Deprotonated and negatively charged.