can u tell me y the following trend is difft. d 1st ionization enthalpy values of gp 13th

Ionisation enthalpy generally decreases down the group. But in this case there is a slight increase in the case of Ga and Th. This is because in case of Ga , 3d subshell is present and in case of Th, 4f subshell is present.

3d and 4f provide poor shielding, so they can't account for the increase in nuclear charge ( which has increased more due to presence of 3d elements and 4f elements resp ).

Therefore , I.E. is more in case of these two..

yes perfectly.... dats the inert pair effect...

by slater's rule,
Z* = Z - shielding constant...

from the values of Z* we can infer the that as there is a dec in value of Z* (Z=atomic no.) there's inc in nuclear charge ... so I.E. is more.