Chemistry · S and p Block Elements

The correct option is D (Positive, positive, negative). This is due to the fact that at pH 3, the environment is acidic, leading to the protonation of the amino group, resulting in a positive charge. At pH 7, while close to the isoelectric point, the environment still causes the molecule to remain positively charged due to partial protonation and deprotonation processes. At pH 11, the environment is basic, causing the amino group to deprotonate, resulting in a negative charge. Options A, B, and C are incorrect as they misinterpret how pH affects the ionization state of the amino acid.

Option A is incorrect because at pH 3, the amino acid is in an acidic environment where the amino group is protonated, resulting in a positive charge. At pH 7, near the pI, the molecule tends to be neutral. But at pH 11, in a basic environment, the molecule tends to be negatively charged, not neutral. 

Option B is incorrect because at pH 3, the amino acid should be positively charged due to the protonation of the amino group. At pH 11, the environment is basic, causing the molecule to be negatively charged. 

Option C is incorrect because at pH 3, the amino acid is in an acidic environment, meaning the amino group will be protonated, resulting in a positive charge. At pH 11, the molecule will not be positively charged but negatively charged due to deprotonation. 

Option D is correct. At pH 3, the amino acid is positively charged as the amino group is protonated. At pH 7, it is close to its isoelectric point, but still in a more acidic environment, where it remains positively charged. At pH 11, the environment is basic, leading to deprotonation and a negative charge.