Why are d and f block elements called transition and inner transition elements respectively?

D and f block elements are called transition and inner transition elements respectively due to their electron configurations.

The d block elements, also known as transition metals, are named so because they are positioned between the s and p block elements in the periodic table. The term 'transition' is used because the properties of these elements often transition, or change, between those of the s block elements (mainly metals) and the p block elements (non-metals and semi-metals). This transition is due to the filling of the d orbitals in their electron configurations. The d block elements have partially filled d orbitals in their ground state or in one or more of their oxidation states. This results in the characteristic properties of transition metals such as variable oxidation states, formation of coloured ions, and catalytic activity.

The f block elements, on the other hand, are referred to as inner transition metals. This is because they are positioned in between the s and d block elements in the periodic table, and their properties transition between those of the s block elements and the d block elements. The f block elements have partially filled f orbitals in their electron configurations. The filling of the f orbitals occurs in the 4f and 5f series, which are placed at the bottom of the periodic table. These elements are further divided into the lanthanides (elements 58-71) and the actinides (elements 90-103). The lanthanides are characterised by the filling of the 4f orbitals, while the actinides are characterised by the filling of the 5f orbitals.

The electron configurations of the d and f block elements, and the resulting properties, are what distinguish them as transition and inner transition elements respectively. Understanding these electron configurations and the resulting properties is key to understanding the behaviour and characteristics of these elements.