Carbon is important to the structure of macromolecules because it has a valence of 4. what does this mean?

If the mass of the products measured 120g what would the mass of the reactants a. 30g b. 60g c. 120g d. 240g

Determine the reaction and balance the following equations urgent due in the morning

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?