The elements in which ‘d’ or ‘f’ orbitals are incomplete either in the atomic state or in their common ions are called:

B. Transition elements

• Transition elements: These elements (groups 3-12 in the periodic table) have incompletely filled d-orbitals in either their atomic state or in their common ions. This incomplete filling of d-orbitals contributes to their characteristic properties, including variable oxidation states, ability to form colored compounds, and involvement in coordination complexes.