Q.Aminoacids, have both an amino group and a carboxyl group in their structure. Which one of the following is an amino acid?

• An amino acid, by definition, has both an amino group (NH2) and a carboxyl group (COOH) attached to the same carbon, the alpha-carbon.
• Formic acid has only a carboxyl group and no amino group, so it is a simple organic acid, not an amino acid.
• Glycerol is trihydroxy propane - it carries hydroxyl groups, not amino or carboxyl groups.
• Glycolic acid carries a hydroxyl and a carboxyl group, but no amino group.
• Glycine is the amino acid in which the R group attached to the alpha-carbon is simply a hydrogen atom, alongside the amino and carboxyl groups every amino acid carries.

Amino acids are organic compounds built around one central carbon, the alpha-carbon, which behaves like a substituted methane: it holds four attachments - a hydrogen atom, a carboxyl group (COOH), an amino group (NH2), and a variable side chain, the R group. It is the simultaneous presence of both the amino group and the carboxyl group on that same carbon that makes a molecule an amino acid.

Checking each option against this definition:

• Formic acid is simply a carboxylic acid; it has no amino group at all.
• Glycerol is trihydroxy propane, carrying three hydroxyl groups - it has neither an amino nor a carboxyl group, and is in fact the alcohol backbone used to build lipids, not an amino acid.
• Glycolic acid has a hydroxyl group and a carboxyl group, but still no amino group.
• Glycine satisfies the definition completely: its R group is just a hydrogen atom, so the molecule is the alpha-carbon bearing a hydrogen, a carboxyl group, an amino group, and a second hydrogen as the R group - the simplest possible amino acid.

Method: Testing each option against the two-group definition of an amino acid

Whenever a question gives you an explicit definition ('an amino acid has both an amino group and a carboxyl group') and then asks you to identify which option fits it, treat that sentence as a checklist and run every option through it - don't rely on recognising the name alone.

For each candidate molecule, ask two yes/no questions: does it have an amino group (NH2)? Does it have a carboxyl group (COOH)? A molecule needs 'yes' to both to qualify. Formic acid has only the acid group. Glycerol has hydroxyl groups, not amino or carboxyl. Glycolic acid has a hydroxyl and a carboxyl group, but still no amino group - close, but it fails the checklist on one count.

Only the option that clears both checks - having an amino group and a carboxyl group on the same carbon - is the true amino acid. Stating which check each wrong option fails is what turns a guess into a reasoned elimination.