D-block elements.

Description
The d-block elements are often also known as transition metals or transition elements.The d-block is a the portion of the periodic table which contains the element groups 3-12.[1][2] These groups correspond to the filling of the atomic d-orbital subshell, with electron configurations ranging from s2d1 (Group 3) to s2d10 (Group 12). There are however some irregularities in the sequence; for example Cr is s1d5 (not s2d4) and the Group 11 metals are s1d10 (not s2d9), so that the d-subshell is actually complete at Group 11.