When would it be appropriate to use a model instead of a controlled experiment

Which element is the least metallic between cadmium, silver, zinc, or iron?

Can someone me with 3 and 4 plz. this is for masteries test.

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?