Answer:
The energy levels in an atom are similar to the rungs of a ladder, but they get closer together as they get farther from the nucleus. For an electron to move from one energy level to the next higher level, it must gain the right amount of energy. If less than that amount is available, the electron stays where it is.
Explanation:
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I found this is the order of activity in Internet
Mn>Zn>Cr>Fe>Cd>Co>Ni>Pb
You can see that Fe is between Cr and Cd
Cr is more active than Fe and Fe is more active than Cd.
The Fe will displace Cd but not Cr.
Answer:Fe