Why PH3, H2S, H2Se, H2Te, AsH3 do not undergo hybridization ?
In hybridisation we need to have bonding orbitals which have similar energy. The central atom here have vacant d-orbital due to which even when small amount of energy is given out the electrons excite to d-orbitals and can participate in d -p bonding.
In the case of PH3 , H2S , AsH3 etc. the central atom being non-metal have almost have similar electronegativity as that of hydrogen atom. Hence they don't undergo hybridisation.