Which of following is an essential amino acid?

Phenylalanine is an essential amino acid, meaning it cannot be synthesized by the body and must be obtained through diet.

Tyrosine, while important, is a non-essential amino acid because the body can synthesize it from phenylalanine.

Alanine is a non-essential amino acid as the body can produce it on its own.

Arginine is conditionally essential, meaning it is required in specific conditions, such as during growth or illness, but not always essential for all individuals.