The atomic radii of transition elements in a period are.

Explanation

In case of transition elements, the electrons are filled in ( n-1)d-sub-shell and they exert screening effect as a result of which the atomic sized is expected to increase. Thus, as we move from left to the right in a tranisition series, the increase in the magnitude of nuclear charge ( leading to decrease in size ) is almost balanced by the increase in the shielding effect ( leading to increase in size ). Because of these two opposing tendencies, there is a very small change in the atomic size ( or atomic radii ) as we move along the transition series. IN s and p-block elements, as we move along a period the electrons are filled in the valence s and p orbitals. These electrons do not exert as much screening effect as are exerted by the electons present in the d- orbitals. There is a gradual increase in effective nuclear charge leading to decrease in atomic size along a particular period.