magnetic moment of Fe in brown ring complex is 3.87 aprox. with electronic strucure is 3d7(2 paired 3 unpaired) 4s0 since no pushes 1 electron inside {told to us} my question is why it does not pushes other and what is its hybridisationin complex

Dear Student,

Brown ring is formed by the complex, [Fe(H₂O)₅(NO)]SO₄. 
Hybridisation of the complex is as follows :
Valence shell electronic configuration of Fe = [Ar] 3d⁶4s^​2
Valnce shell electronic configuration of Fe²⁺ = [Ar] 3d⁶ 4s⁰
Now since NO is a strong field ligand, so pairing of the 6 electron in d-orbital occurs and gives rise of d²sp³ hybridisation.