The half-cell reaction at the anode during the electrolysis of aqueous sodium chloride solution  is represented by : 

1. Na⁺(aq) + e^- ⟶ Na(s) ; \(E_{cell}^{o} \ = \ -2.71 \ V \)

2. 2H₂O(l) ⟶ O₂(g) + 4H⁺(aq) + 4e^- ; \(E_{cell}^{o} \) = 1.23 V

3. H⁺(aq) + e^- ⟶ \(\frac{1}{2}\)H₂(g) ; \(E_{cell}^{o} \) = 0.00 V

4. Cl^-(aq) ⟶ \(\frac{1}{2}\)Cl₂(g) + e- ; \(E_{cell}^{o}\) $= 1.\mathrm{36 }\mathrm{V}$

During the electrolysis of a highly concentrated H₂SO₄ solution, which is released at the anode?

1. H₂

2. O₂

3. S₂O₈^2–

4. Both (1) & (3)