$C_2H_2$ is isostructural with

Which of the following processes involves a change in bond angle along with a change in hybridization?

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

In which of the following pairs do both the species have $sp^{3}$ hybridization?

When $BCl_3$ is treated with water,it hydrolyses and forms $[B(OH)_4]^-$ only,whereas $AlCl_3$ in acidified aqueous solution forms $[Al(H_2O)_6]^{3+}$ ion. Explain what are the hybridizations of boron and aluminum in these species?

The valency of carbon is $4$. On what principle can it be explained in a better way?