The volume (in mL ) of 10 volume $\mathrm{H}_2 \mathrm{O}_2$ solution required to completely react with 200 mL of 0.4 M $\mathrm{KMnO}_4$ solution in acidic medium is

Observe the following reactions

(i) $2 \mathrm{KClO}_3(s) \xrightarrow{\Delta} 2 \mathrm{KCl}(s)+3 \mathrm{O}_2(g)$

(ii) $2 \mathrm{H}_2 \mathrm{O}_2(a q) \xrightarrow{\Delta} 2 \mathrm{H}_2 \mathrm{O}(l)+\mathrm{O}_2(g)$

(iii) $\mathrm{AgNO}_3(a q)+\mathrm{KCl}(a q) \longrightarrow \mathrm{AgCl}(s)+\mathrm{KNO}_3(a q)$

(iv) $2 \mathrm{Na}(s)+\frac{1}{2} \mathrm{O}_2(g) \longrightarrow \mathrm{Na}_2 \mathrm{O}(s)$

The number of redox reactions in thsi list is