Write the molecular equation including the state (s, l, g, aq) for every reactant and product.

a) C2H4(g) + H2(g) -> C2H6(g)
b) 2H2(g) + O2(g) -> 2H2O(l)
c) HCl(g) + NaOH(aq) -> NaCl(aq) + H2O(l)
d) CaCO3(s) -> CaO(s) + CO2(g)