We are given
Ox: Sn(s) → Sn2+ (aq, 1.85 M) + 2e−
Red: ClO2 (g, 0.150 atm ) + e− → ClO−2 (aq, 2.00 M)
We are to compute the cell potential at 25 °C
We simply have to look for the standard potentials for each of the reactions and subtract the redox standard potential from the oxidation standard potential.
From literature and after doing the operation, the answer is
Ecell = 2.2 V