What is the hybridisation state of the central atom and the shape of the conjugate base of the ammonium ion?

$A$ molecule is square planar and has no lone pairs. What type of hybridization is it associated with?

During the conversion of $PCl_3$ to $PCl_5$,the hybridisation of the $P$ atom changes from .......

The outer orbitals of $C$ in ethene molecule can be considered to be hybridized to give three equivalent $sp^2$ orbitals. The total number of sigma $(\sigma)$ and pi $(\pi)$ bonds in ethene molecule is

Among the triatomic molecules/ions,$BeCl_2, N_3^{-}, N_2O, NO_2^{+}, O_3, SCl_2, ICl_2^{-}, I_3^{-}$ and $XeF_2$,the total number of linear molecule$(s)$/ion$(s)$ where the hybridization of the central atom does not have contribution from the $d$-orbital$(s)$ is
[Atomic number: $S=16, Cl=17, I=53$ and $Xe=54$ ]

What is the $C - C$ bond length in molecules with $sp^2$ hybridization (in $\mathring{A}$)?