Explanation:

- Proteins play a crucial role in metabolic reactions as they act as enzymes. Enzymes speed up chemical reactions in the body, essential for metabolism.

- Correct Answer: Option 1: Proteins

- Carbohydrates mainly serve as a source of energy, not as catalysts for reactions.

- Lipids are important for long-term energy storage and cell membrane structure, not directly involved in catalyzing reactions.

- Salts maintain balance of fluids and electrolytes but do not catalyze metabolic reactions.