The reaction s that are redox reactions are
4Li(s) +O2 (g)→ 2Li2O (s)\
Mg(s) + Fe2+ (aq)→ Mg2+(aq) + Fe(s)
A redox reaction involve both oxidation and reduction. During redox reaction there is change in oxidation states. For example in
4Li +O2 →2Li2O Li is oxidized while O is reduced
in Mg +Fe2+ → Mg2+ +Fe Mg is oxidized since it move from oxidation state 0 to 2+ while Fe2+ is reduced since it move from oxidation state of 2+ to 0