Which of the following amino acids contains a positively charged side chain at a pH of 7.0?

✅Explanation:
At a physiological pH of 7.0, the side chains of amino acids can be charged depending on their pKa values. Arginine has a positively charged side chain at this pH because its guanidinium group remains protonated.

📌Other Options Explanation:

a) Glutamic acid:
-Glutamic acid has a negatively charged side chain at pH 7.0 because its carboxylic acid group is deprotonated (pKa ~4.3).

(c) Tyrosine:
-Tyrosine has a phenolic hydroxyl group in its side chain, which has a pKa ~10.1. At pH 7.0, this group remains neutral.