sp3d3 count the no of sigma bonds. and in k2cr2o7 the hybridization state of cr is sp3 again c the structure in 12th's ncert and count the no of sigma bond
ha ha ha ha ha fst of all i haven't heard of IF72- the compound is IF7 n its hybridization state is Sp3d3...u can check in jd lee and inorganic chemistry by satya prakash.
n the hybridization state of Cr in dichromate is Sp3 itmeans shape is tetrahedral. that u can check in jdlee page no 788.