The standard reduction potential data at 25∘C are E∘(FeX3+,FeX2+)=+0.77V, E∘(FeX2+,Fe)=−0.44V, E∘(CuX2+,Cu)=+0.34V, E∘(CuX+,Cu)=+0.52V, E∘[OX2(g)X4+HX++4eX−2HX2O]=+1.23V, E∘[OX2(g)X2+HX2OX4+eX−4OHX−]=+0.40V, E∘(CrX3+,Cr)=−0.74V and E∘(CrX2+,Cr)=−0.91V. Match List I with List II.
Column I — P: E∘(FeX3+,Fe); Q: E∘(4HX2O4HX++4OHX−); R: E∘(CuX2++Cu2CuX+); S: E∘(CrX3+,CrX2+)Column Ii — 1: −0.18V; 2: −0.40V; 3: −0.04V; 4: −0.83V