The types of hybridization that take place in the central atom of the species  ${\mathrm{NH}}_4^{+},{\mathrm{BF}}_4^{-}$ and ${\mathrm{BeCl}}_2$ respectively are :

The nitrogen atom needs 4 hybrid orbitals because it makes 4 bonds and has 0 lone pairs. As a result, ${\mathrm{BF}}_4^{-}$ is in the ${\mathrm{sp}}^3$ hybridization state since it has 4 bond pairs and 0 lone pairs.

${\mathrm{BeCl}}_2$ a beryllium atom forms a single covalent link with two chlorine atoms. There will be two electron pairs surrounding the main atom. The molecule does not include any lone pairs. We can infer from this data's analysis that , ${\mathrm{BeCl}}_2$ has sp.