Which element is used to treat indigestion and stomach acidity?

Calcium Carbonate is the active ingredient in Tums, so is a valid choice.

I remember Milk of Magnesia - not in a good way.

CaCO3 is also an option,so the question is not correct.

Most adults are magnesium deficient, foods are becoming less nutritious for many reasons such as soil depletion and food processing.

yes milk of magnesia instantly feel good