The elements of the groups 3 to 12 are called ______ elements or transition elements.

d-block

The correct answer is option 2. d-block.

The elements of groups 3 to 12 in the periodic table are known as the d-block elements or transition elements. Here's an explanation:

1. Location in the Periodic Table:

The periodic table is divided into several blocks based on the electron configuration of elements. The d-block is one of these blocks, and it includes the elements found in groups 3 to 12.

2. Electron Configuration:

The defining characteristic of d-block elements is that they have electrons filling their \(n-1\) d orbitals, where \(n\) is the principal quantum number of the electron shell. For example, in the fourth period, the d-block elements have electrons filling the 3d orbitals.

3. Transition Elements:

The term "transition elements" is often used interchangeably with "d-block elements." These elements are characterized by the filling of their d orbitals as they transition from one electron configuration to the next.

Transition elements are found in the central part of the periodic table, between the s-block (groups 1 and 2) and the p-block (groups 13 to 18).

In summary, the d-block elements, also known as transition elements, occupy the central region of the periodic table and are characterized by the filling of their d orbitals. They play a crucial role in various chemical reactions and have diverse applications in different fields.