Transition elements show variable oxidation states mainly because ____.
Correct answer A. the 3d and 4s electrons are close in energy and both can be used in bonding
Explanation
The 4s and 3d subshells have similar energies, so different numbers of electrons can be lost or shared with only small energy differences. This gives a range of stable oxidation states, for example Fe²⁺ and Fe³⁺.
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