Which of the following statements are correct regarding amino acids...

Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon, i.e., the $\alpha$-carbon. Therefore, they are considered substituted methanes. Statement A is correct.

Serine contains a hydroxymethyl group ($\text{-CH}_2\text{OH}$) as its side chain and is an aliphatic amino acid, not an aromatic one. Aromatic amino acids include phenylalanine, tyrosine, and tryptophan. Statement B is incorrect.

Valine contains one amino group and one carboxyl group, making it a neutral amino acid. Statement C is correct.

Lysine contains two amino groups and one carboxyl group, making it a basic amino acid, not an acidic one. Acidic amino acids include aspartic acid and glutamic acid. Statement D is incorrect.

Thus, only statements A and C are correct.

Answer: A and C only