Answer: The correct answer is Iron (Fe).
Explanation:
When a metal displaces another metal from a solution, it is considered as a reactive metal and the reactivity of metal is judged by the reactivity series of the metal.
Whenever one metal displaces another metal from its salt solution, it is considered as a Single-displacement reactions.
In a reactivity series, the metal which is present above in the series will easily displace a metal which is present below in the series.
We need to find an unknown metal which easily displaces cadmium metal from a solution which means that a metal is present above in the reactivity series and the same metal does not displace chromium which means that it is present below chromium. Hence, the unknown metal is iron.
Reactivity series is attached below.
