Question

lithium does not show back bonding why????????

Answer 1

For black bonding an atom must have lone pair and another atom must aslo have vacant orbital in its valence shell.

But lithium doesn't have these properties

Answer 2

$\underline{\underline{\Huge\mathfrak{Answer}}}$

As we know that electronegativity substituents exhibit greater π backbonding.
Therefore, strong π backbonding ligands are tetrafluoroethylene and so on.