Saw dust is used to adulterate:

coriander powder

The correct answer is option 3. coriander powder.

Sawdust is sometimes used as an adulterant in coriander powder to increase the bulk and weight of the product without adding significant cost.

While sawdust can be used in other applications like cleaning or as an absorbent, it is not commonly used to adulterate the other options listed:

Vinegar: Vinegar is typically adulterated with water or acetic acid of lower concentration, not sawdust.

Cheese: Cheese can be adulterated with various substances like starches, fats, or even chalk, but not typically sawdust.

Milk: Milk can be adulterated with water, but not sawdust due to its obvious physical differences.

It's important to note that adulteration is illegal and harmful as it reduces the quality and safety of the food product.