What do oxygen and iron make?

What substance has a mass of 9.5g and volume of 2.1cm^3

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?

Structure of the atoms: discovery of the nucleus in 1909i need answering all of these questions