How can I calculate hybridization of an atom?
The easiest way to get at hybridization is the know how to do the electron geometry (shape of molecules including the electron pairs). If a molecule is linear, it is sp hybridized; trigonal planar, sp2 hybridized; tetrahedral, sp3 hybridized; trigonal bipyramidal, sp3d1 hybridized; and octahedral, sp3d2 hybridized.
Again, these are for electron geometries. Ammonia, NH3 has molecular geometry of pyramidal, but its electron geometry is tetrahedral, so it is sp3 hybridized.