Help ASAP synthesis or decomposition

1. 2K(s) + Cl2(g) - 2KCl(s)

2. FeS(s) - Fe(s) + S(s)

3. 2Mg(s) + O2(g) - 2MgO(s)

4. 2H2(g) - O2(g)-2H2O(l)

5. CaCO3(s)- CaO(s) + CO2(g)

answer; i believe the correct answer is (solid gold);

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error

fe 55.85 g/mol and h2o 18.02 g/mol.