In which pair of ions both the species contain S-S bond?

1. ${\mathrm{S}}_2{\mathrm{O}}_7^{2-},$ ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}$

2. ${\mathrm{S}}_4{\mathrm{O}}_6^{2-},$ ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$

3. ${\mathrm{S}}_4{\mathrm{O}}_6^{2-},$ ${\mathrm{S}}_2{\mathrm{O}}_7^{2-}$

4. ${\mathrm{S}}_2{\mathrm{O}}_7^{2-},$ ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$

Hot concentrated sulphuric acid is a moderately strong oxidising agent. Which of the following reaction doe not show oxidising behaviour?

(a) Cu + 2H₂SO₄ $\to$CuSO₄ + SO₂ + 2H₂O

(b) 3S + 2H₂SO₄ $\to$3SO₂ + 2H₂O

(c) C + 2H₂SO₄ $\to$CO₂ + 2SO₂ + 2H₂O

(d) CaF₂ + H₂SO₄ $\to$CaSO₄ + 2HF

Which of the following reactions does not exhibit the oxidising behaviour of H₂SO₄?

1. Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O

2. 3S + 2H₂SO₄ → 3SO₂ + 2H₂O

3. C + 2H₂SO₄ → CO₂ + 2SO₂ + 2H₂O

4. CaF₂ + H₂SO₄ → CaSO₄ + 2HF