The species in which the central atom uses $sp^2$ hybrid orbitals in its bonding is

In the compound $CH_3COCl$,which type of orbitals have been used by the carbonyl carbon in bond formation?

Define the following terms:
$(i)$ Hybridisation
$(ii)$ $sp$ Hybridisation
$(iii)$ $sp^2$ Hybridisation
$(iv)$ $sp^3$ Hybridisation
$(v)$ Hydrogen bonding

Of the following compounds,the one having a linear structure is

Describe the hybridization in $PCl_{5}$. Why are the axial bonds longer as compared to equatorial bonds?

Which of the following statements is true regarding the $PCl_5$ molecule?
$(i)$ The two axial $P-Cl$ bonds in $PCl_5$ are longer than the three equatorial bonds.
$(ii)$ The axial bonds in $PCl_5$ are stronger than equatorial bonds.
$(iii)$ The axial bonds in $PCl_5$ are more stable than equatorial bonds.
$(iv)$ All five bonds in $PCl_5$ molecule are equivalent.