To how much water should 250 mL of 12 M hydrochloric acid be added to
produce a 4.0 M solution?

500ml water

Explanation:

Molarity x Volume in liters (concentrated soln) = Molarity x Volume (diluted soln) ∴

250ml X 12M HCl =  4M x Volume of diluted solution

=> Volume of diluted solution = (250ml)(12M)/(4m) = 750 ml final solution vol. after mixing.

So the amount of water added to the 250ml of 12M acid = 750ml - 250ml = 500ml of water.

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.