A transition element is best defined as one that
- A. lies between groups II and III of the periodic table
- B. forms at least one stable ion with a partially filled d subshell
- C. has a full d subshell
- D. is a hard metal with a high melting point
Explanation
The definition rests on the partially filled d subshell in the element or in one of its ions, because that is what produces variable oxidation states, coloured ions, catalytic activity and complex formation. Zinc is excluded on this test, since it is 3d10 both as the atom and as the Zn2+ ion, which is why it lacks colour and variable valency. Position in the table and physical hardness are consequences rather than the definition.
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