The correct answer is option 4, which states that all of the substances listed - pesticide residues, lead, metanil yellow, and mercury - are harmful to health if present in food items.

To understand why these substances are harmful, let`s look at each one individually:

1. Pesticide residues: Pesticides are chemicals used to kill or control pests like insects, weeds, and fungi. If pesticide residues remain on or in food items, they can pose a risk to human health. Prolonged exposure to pesticides has been linked to various health issues, including cancer, reproductive problems, and damage to the nervous system.

2. Lead: Lead is a toxic heavy metal that can contaminate food, particularly through storage or cooking processes involving lead-containing materials. Long-term exposure to lead can cause developmental and neurological damage, leading to learning difficulties, behavioral problems, and organ damage.

3. Metanil yellow: Metanil yellow is an artificial dye that is sometimes used illegally to enhance the color of food items. It is toxic and carcinogenic, meaning it can cause cancer if consumed. Ingesting food contaminated with metanil yellow can lead to health issues like liver damage and stomach problems.

4. Mercury: Mercury is a heavy metal that