Q$2$:

Classification of ligands according to number of electrons to the bonding with transition metals

$\backslash$table$[[\backslash$table$[[$Electrons$],[$contributed$]],$Ligands$],[H,$ alkyl $,$ aryl $,$ acyl $,{}^1-$ allyl groups$],[$Olefin $,$CO$,$ simple Lewis bases $,P{R}_3,$ carbenes $($:$C{R}_2)$