What is one way to describe elements? a. building blocks b. they break down easily c. smallest particles of material d. they are the most expensive materials on earth

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?