Why does matter (or the mass that makes it up) never "go away?"

Calculate the molarity of each of the following solutions. part a) 0.12 mol of lino3 in 5.5 l of solution part b) 60.7 g c2h6o in 2.48 l of solution part c) 14.2 mg ki in 100 ml of solution

An atom of which element reacts with an atom of hydrogen to form a bond with the greatest degree of polarity ?

When the chemicals iron sulfide (fes) and hydrochloric acid (hcl) are combined, bubbles appear from the mixture. 1. does the appearance of bubbles indicate a physical or chemical change? 2. why do the bubbles indicate this change? 3. what property is this?