If the E°cell is lower, then E°cell of Cr and Pb can be reduced/cannot be oxidized.
Cr/Cr2+ → E°cell = -0.26 V
Pb/Pb2+ → E°cell = -0.913 V
Inspecting the choices:
Br-, Ca and Co are reduced form so these cannot be OA anymore
Which of the following reagents would oxidize Cr to Cr2+, but not Pb to Pb2+?
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