To solve this problem, we need to identify which of the given amino acids is basic.$\newline$Amino acids can be classified as acidic, basic, or neutral based on the nature of their side chains.$\newline$Let's analyze each option:$\newline$• Alanine:$\newline$ - Alanine has a nonpolar, neutral side chain (a methyl group).$\newline$• Tyrosine:$\newline$ - Tyrosine has a polar side chain with a phenolic hydroxyl group, making it neutral.$\newline$• Lysine:$\newline$ - Lysine has a side chain with an amino group, which is basic.$\newline$ - The amino group can accept a proton, giving lysine a positive charge at physiological pH.$\newline$• Serine:$\newline$ - Serine has a polar side chain with a hydroxyl group, making it neutral.$\newline$Based on the analysis, lysine is the only amino acid with a basic side chain.$\newline$Therefore, the correct option is Option 3: Lysine.