Question

why 4d, 5d transition elements have stable higher oxidation states

Answer 1

Transition elements are metallic elements that have incomplete d or f shells in the
neutral or cationic states. They are called also transition metals and make up 56 of the
103 elements. These transition metals are classified into the d-block metals, which
consist of 3d elements from Sc to Cu, 4d elements from Y to Ag, and 5d elements from Hf
to Au, and f-block metals, which consist of lanthanoid elements from La to Lu and
actinoid elements from Ac to Lr. Although Sc and Y belong to the d-block, their proper-
ties are similar to those of lanthanoids. The chemistry of d-block and f-block
elements differs considerably. This chapter describes the properties and chemistry of
mainly d-block transition metals.