What is the oxidation number of sulfur in Na_2SO_4 ?
Which of the reactions below are redox?
I. 2 Al(s) + 3 CuCl _2 (aq) --> 2 AlCl _3 (aq) + 3 Cu(s)
II. 2 Al(s) + 6 HCl(aq) --> 2 AlCl _3 (aq) + 3 H _2 (g)
III. 2 H _2 (g) + O _2 (g) --> 2 H _2 O(g)