What is the enzyme responsible for lactose breakdown ?

Lactase 

The correct answer is Option (3) - Lactase
Lactose is a sugar found in milk and milk products. Lactose intolerance happens when your small intestine does not make enough of a digestive enzyme called lactase.

Lactase breaks down the lactose in food so your body can absorb it.

People who are lactose intolerant have unpleasant symptoms after eating or drinking milk or milk products.

These symptoms include bloating, diarrhea and gas.