Total number of redox reactions among the given reactions is
i. `CaO + SO_(3) rarr CaSO_4`
ii. `4Cu + O_2 rarr 2 Cu_(2) O`
iii. `MgO + CO_2 rarr MgCO_3`
iv. `SO_2 + H_2Orarr H_(2)SO_3`
v. `2 KClO_(3(s))overset(Delta)rarr2 KCl_((s))+3O_(2(g))`
vi. `3 Mg_((s)) + N_(2(g))overset(Delta)rarrMg_(3) N_(2(s))`
vii. `Cr_(2)O_(3(s)) +2Al_((s))overset(Delta)rarrAl_(2)O_(3(s))+2Cr_((s))`
viii. `2H_2O_((l))+2F_(2(g))rarr4HF_((aq))+O_(2(g))`

Answer

5

Explanation

Reactions ii, v, vi, vii, viii are redox reactions.