Step 1: Understanding Essential Amino Acids.
- Amino acids are organic compounds containing amino (-NH\(_2)\) and carboxyl (-COOH) functional groups.
- Essential amino acids cannot be synthesized by the human body and must be obtained from dietary sources.
Step 2: Identifying the Essential Amino Acid.
- Valine (\(H_2N-CH(CH_3)_2-COOH\)) is an essential amino acid.
- It is necessary for muscle growth, tissue repair, and energy production.
- The other given options include:
- Alanine (\(H_2N-CH(CH_3)-COOH\)) – a non-essential amino acid.
- Serine (\(H_2N-CH_2OH-COOH\)) – a non-essential amino acid.
- Cysteine (\(H_2N-CH_2SH-COOH\)) – a non-essential amino acid.
Step 3: Conclusion.
Since valine is an essential amino acid that must be obtained through diet, option (3) is correct.