Given Zn2+→Zn‌E∘=−0.78V Cu2+→Cu‌E∘=0.34V Ag+→Ag‌E∘=0.8V Cell reaction of (1) is ‌Zn+Cu2+→Zn2++Cu ‌E‌cell ‌∘=E‌oxidation ‌+E‌reduction ‌ ‌=+0.78+0.34 ‌=+1.12V Cell reaction of (2) is Zn+Ag+‌→Zn2++Ag E‌cell ‌∘‌=0.78+0.8 ‌=+1.58V Cell reaction of (3) is : Cu+Ag+‌→Cu2++Ag E‌cell ‌∘‌=−0.34+0.8 ‌=+0.46 So, the correct order of E∘ cell of these cell is - b>a>c.