What do you understand by $(i)$ electron-deficient,$(ii)$ electron-precise,and $(iii)$ electron-rich compounds of hydrogen? Provide justification with suitable examples.

(N/A) Molecular hydrides are classified on the basis of the total number of electrons and bonds in their Lewis structures as:
$1.$ Electron-deficient hydrides: These have fewer electrons than required for writing their conventional Lewis structures. Example: Diborane $(B_2H_6)$. In $B_2H_6$,there are six bonds in total,out of which only four are regular two-centered-two-electron bonds. The remaining two are three-centered-two-electron bonds,meaning two electrons are shared by three atoms.
$2.$ Electron-precise hydrides: These have a sufficient number of electrons to be represented by their conventional Lewis structures. Example: Methane $(CH_4)$. It forms four regular bonds where two electrons are shared by two atoms.
$3.$ Electron-rich hydrides: These contain excess electrons as lone pairs. Example: Ammonia $(NH_3)$. It has three regular bonds and one lone pair of electrons on the nitrogen atom.