What are p-pi - p-pi , p-pi - d-pi and d-pi - d-pi bonds.....????

Answer :

If there is bonding between two atoms where one atom is having one vacant orbital and another is having one lone pair of electrons, then if this electron pair is donated to that respective vacant orbital then the bonding is called p(pie) - p(pie) or p(pie) - d(pie) depending on the orbital to which the electron pair is donated and from which the electron pair is donated. If both the orbitals are d orbitals, then bonding is called d(pie) - d(pie) bonding.