The metal you can insert in aqueous solution of cobalt(ii) nitrate and displace cobalt is zinc.
Electrochemical series
Electrochemical series is as know as reactivity series. The electrochemical series list metals in order of decreasing reactivity.
Generally, metals higher up in the series than cobalt metal will displace cobalt(ii) ions from it solution and produce cobalt metal. Therefore, Metals like Zinc will displace cobalt(ii) form it compound.
The reaction with a solution of cobalt (II) nitrate can be represented as follows:
Co(NO₃)₂ + Zn → Zn(NO₃)₂ + Co
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