Which of the following is an amino group?

• A. $-C{O}_{2}H$
• B. $-N{H}_2$
• C. $-OH$
• D. $-SH$

Answer: (B)

Verified step by step guidance

1. Identify the functional groups given in the problem by their chemical formulas: -CO2H, -NH2, -OH, and -SH.
2. Recall that an amino group is characterized by a nitrogen atom bonded to hydrogen atoms, typically represented as -NH2.
3. Analyze each group: -CO2H is a carboxyl group, containing carbon, oxygen, and hydrogen; -OH is a hydroxyl group; -SH is a thiol group.
4. Confirm that the group containing nitrogen bonded to two hydrogens, -NH2, matches the definition of an amino group.
5. Conclude that among the options, the amino group is represented by the formula \(-\mathrm{NH}_{2}\).