Which of the following statements are correct regarding amino acids ?

A. They are substituted methanes.

B. Serine is an aromatic amino acid.
C. Valine is a neutral amino acid.
D. Lysine is an acidic amino acid.

Choose the correct answer from the options given below :

**Statement A:** “They are substituted methanes.”

Every α‑amino acid has a central carbon atom (the α‑carbon) bonded to four groups: a hydrogen atom, an amino group (–NH₂), a carboxyl group (–COOH), and a distinctive side chain (R). This structure can be viewed as a methane molecule (CH₄) in which three of the hydrogen atoms are replaced by the amino, carboxyl, and side‑chain groups. Hence amino acids are indeed “substituted methanes,” making statement A correct.

**Statement B:** “Serine is an aromatic amino acid.”

Serine’s side chain is –CH₂OH, a simple aliphatic alcohol. Aromatic amino acids contain a benzene‑like aromatic ring (e.g., phenylalanine, tyrosine, tryptophan). Since serine lacks such a ring, it is not aromatic. Therefore statement B is false.

**Statement C:** “Valine is a neutral amino acid.”

Valine’s side chain is –CH(CH₃)₂, a branched, non‑polar group. At physiological pH (≈7.4) valine carries no net charge; it is classified as a neutral (non‑polar) amino acid. Thus statement C is correct.

**Statement D:** “Lysine is an acidic amino acid.”

Lysine possesses a side chain ending in an ε‑amino group (–NH₃⁺) that is positively charged under physiological conditions, making it a basic (positively charged) amino acid, not acidic. Consequently, statement D is false.

Combining the evaluations, the only correct statements are **A** and **C**.