Use valence bond theory to describe the bonding and geometry in the sef4 molecule.

a. the central atom is se, which has five electron groups around it (four bonding pairs and one nonbonding/lone pair). the electron-group geometry is trigonal bipyramidal (and the molecular geometry is see-saw). to facilitate this geometry, the se atom's orbitals are hybridized as sp3d orbitals. four of these hybrid orbitals contain one of se's 6 valence electrons each, and these hybrid orbitals overlap with unhybridized p orbitals of the four f atoms. the fifth hybrid orbital of se contains a lone pair of electrons. there are 4 sigma bonds and 0 pi bonds in this molecule.
b. the central atom is se, which has six electron groups around it. the electron-group geometry is octahedral. to facilitate this geometry, the se atom's orbitals are hybridized as sp3d2 orbitals. four of these hybrid orbitals contain one of se's 6 valence electrons each, and these hybrid orbitals overlap with unhybridized p orbitals of the four f atoms. the fifth and sixth hybrid orbitals of se contain lone pairs of electrons. there are 4 sigma bonds and 0 pi bonds in this molecule.
c. the central atom is se, which has four electron groups around it. the electron-group geometry is tetrahedral. to facilitate this geometry, the se atom's orbitals are hybridized as sp3 orbitals. these hybrid orbitals overlap with unhybridized p orbitals of the four f atoms. there are 4 sigma bonds and 0 pi bonds in this molecule.
d. the central atom is se, which has four electron groups around it, two single bonds and two double bonds. the electron-group geometry is tetrahedral. to facilitate this geometry, the se atom's orbitals are hybridized as sp3 orbitals. these hybrid orbitals contain one electron each of se's 6 valence electrons, and these hybrid orbitals overlap with unhybridized p orbitals of the four f atoms. the final 2 electrons of se's 6 valence electrons reside in unhybridized p orbitals, which overlap with unhybridized p orbitals of the f atoms. there are 4 sigma bonds and 2 pi bonds in this molecule.