D-block elements are chemical elements having electrons filling to their d orbitals. All transition metals are d-block elements but all d-block elements are not transition elements because all d- block elements which don’t have completely filled d- orbitals are not counted as transition, so such elements are exceptional. Transition elements are chemical elements that have incompletely filled d orbitals at least in one stable cation they form.
Example: Zn, Cd, and Hg are d-block elements but not transition metals.