Final answer:
The isoelectric point of lysine, a basic amino acid with a positively charged side chain, would most closely be option D. 12, due to its higher pH requirement for neutrality.
Step-by-step explanation:
The isoelectric point (pl) of an amino acid is the pH at which the molecule is electrically neutral, with equal positive and negative charges. Basic amino acids like lysine, which have positively charged side chains, tend to have relatively high isoelectric points because they require a higher pH to reach a state where the positive and negative charges balance each other out. In contrast, acidic amino acids have lower isoelectric points. Considering lysine is a basic amino acid with a basic side chain, its isoelectric point would be closest to the higher end of the pH scale provided in the options.
Therefore, the isoelectric point of lysine would be closest to: D. 12, which is much higher than the neutral pH of 7 and in the range of where basic amino acids have their isoelectric points.