Mention any three ways of making salt. (please help me Asap)

Which of the following is a compound? a.carbon b.oxygen c.hydrogen d.water

What does a numerical subscript following an element in a chemical formula mean?

Calcium carbonate decomposes at high temperatures to give calcium oxide and carbon dioxide as shown below. caco3(s) cao(s) + co2(g) the kp for this reaction is 1.16 at 800°c. a 5.00 l vessel containing 10.0 g of caco3(s) was evacuated to remove the air, sealed, and then heated to 800°c. ignoring the volume occupied by the solid, what will be the mass of the solid in the vessel once equilibrium is reached?