Answer
To locate the position of cadmium in the activity series, you would be most advised to place a strip of pure iron in an aqueous cadmium chloride (CdCl$_{2}$) solution. If solid cadmium is deposited onto the iron strip, this indicates that the Cd is less active than the Fe. However, if there is no reaction at all, this indicates the opposite: Cd is more active than Fe.
If Cd is less active than Fe, the same test should be conducted with Co. If Cd is more active than Fe, the same test should be performed with Cr.
Work Step by Step
To locate the position of cadmium in the activity series, you would be most advised to place a strip of pure iron in an aqueous cadmium chloride (CdCl$_{2}$) solution. If solid cadmium is deposited onto the iron strip, this indicates that the Cd is less active than the Fe. However, if there is no reaction at all, this indicates the opposite: Cd is more active than Fe.
If Cd is less active than Fe, the same test should be conducted with Co. If Cd is more active than Fe, the same test should be performed with Cr.
