$(a)\;H_2(g)+I_2(g) \to 2HI(g)\\(b)\; HCl(ag)+NaOH (ag) \to NaCl(ag)+H_2O(l)\\(c)\;C(s)+O_2(g) \to CO_2(g) \\(d)\;N_2(g)+3H_2(g) \to 2NH_3(g) $
