Which of the following is an essential amino acid?

Leucine

The correct answer is Option (3) → Leucine.

Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet. The other options listed are non-essential amino acids, which the body can produce on its own.

Leucine is an essential amino acid, meaning it must be obtained from food sources like meat, dairy, eggs, and legumes.

Aspartic Acid, Alanine, and Proline are non-essential amino acids, meaning the body can synthesize them.

Summary:

Leucine is essential and must be acquired through diet.The other amino acids (Aspartic Acid, Alanine, Proline) are non-essential.