Why does the size of d-block elements decrease gradually in the periodic table?

Answer 1

As increase in proton number, the attraction from nucleus towards electrons increased. This will pull the electrons stongly. So, the size/ atomic radius decreased across the d-block.

Answer 2

The size of d-block elements gradually decreases across a period due to increasing effective nuclear charge, which attracts the valence electrons more strongly, leading to a smaller atomic radius. Additionally, there is poor shielding of the nuclear charge by inner shell electrons in these elements, contributing to the decrease in size.