⭐ Elements in which the last electron enters any one of the five d-oribitals of their respective penultimate shells are called as <u>d-block</u><u> </u><u>elem</u><u>ents</u> .
⭐ But the last electron of Zn , Cd , Hg and Cn enters in the s-oribital of their respective ultimate shells rather than the d-oribitals of their respective penultimate shells . Therefore, these elements cannot be regarded as d-block elements .
☃️ But properties of these elements resemble to the d-block elements rather than s-block elements .
☃️ Therefore, to make the study of periodic classification of elements more rational, they are studied along with d-block elements .
✍️ Thus <u>on the basis of properties</u> all transition elements are d- block elements, but <u>on the basis of electronic configuration</u> all d -block elements are not transition elements .