Explanation:
Amino acids are organic compounds that serve as the building blocks of proteins. They have an amino group (-NH2) and a carboxyl group (-COOH) attached to a central carbon atom. The side chain, or R-group, varies for each amino acid and determines its unique properties.

Absorbance at 280 nm:
The absorbance at 280 nm is commonly used to measure the concentration of proteins and peptides in solution. This is because the aromatic amino acids, particularly tryptophan, tyrosine, and phenylalanine, have strong absorbance in the ultraviolet region due to their aromatic rings.

Tryptophan:
Tryptophan is an essential amino acid and has the highest absorbance at 280 nm among the three aromatic amino acids. This is because tryptophan has a large indole side chain, which contains a double bond and a nitrogen atom within its aromatic ring structure. These features contribute to its strong absorbance in the ultraviolet region.

Phenylalanine:
Phenylalanine is also an essential amino acid and has a phenyl side chain. Although it has an aromatic ring, it has a lower absorbance at 280 nm compared to tryptophan. This is because the side chain lacks the double bond and nitrogen atom present in tryptophan's indole ring.

Tyrosine:
Tyrosine is a non-essential amino acid and has a hydroxyl group (-OH) attached to its phenyl side chain. Like phenylalanine, it has an aromatic ring but with an additional hydroxyl group. This hydroxyl group slightly increases the absorbance at 280 nm compared to phenylalanine, but it still has a lower absorbance than tryptophan.

Alanine:
Alanine is a non-aromatic, non-polar amino acid with a small methyl side chain. It does not have any absorbance at 280 nm since it lacks an aromatic ring.

In conclusion, among the given amino acids, tryptophan shows the highest absorbance at 280 nm due to its large indole side chain. Phenylalanine and tyrosine have lower absorbance at this wavelength, while alanine does not have any absorbance at all.