The correct answer is option 3, FSSAI.

Option 1, FDA (Food and Drug Administration), is an agency in the United States that enforces food safety regulations. It does not have jurisdiction or authority in India.

Option 2, WHO (World Health Organization), is a global organization that focuses on public health. While WHO does provide guidance and recommendations on food safety, it does not have the power to enforce laws on food security in any particular country.

Option 4, PAO (Public Accounts Office), is responsible for auditing and maintaining government accounts in India. It does not have any role in enforcing food security laws.

Therefore, the correct agency that enforces the laws on food security in India is option 3, FSSAI (Food Safety and Standards Authority of India). FSSAI is a regulatory body under the Ministry of Health and Family Welfare, Government of India, and is responsible for setting standards for food products and ensuring their safety and quality.