Chromium is classified as a transition element because
A it is in the d block of the Periodic Table.
B it forms stable ions in which it has different oxidation numbers.
C it has incompletely filled d orbitals.
D it forms stable ions which have incompletely filled d orbitals.
The only correct answer is D
A is not correct because not all d block metals are transition elements.
B is not correct because the definition should refer to incompletely filled d orbitals.
C is not correct because it must refer to ions, not just the atoms of the element.
