In $but-2-ene$, which one of the following statements is true?

Which one amongst the following possesses an $sp$ hybridized carbon in its structure?

Number of pure $p-$ orbitals in the given molecule $\text{hexa-}1, 3-\text{dien-}5-\text{yne}$.

In the compound $HC \equiv C-CH=CH_2$, the hybridization of $C-2$ and $C-3$ carbons are respectively:

Allyl isocyanide contains $......... \sigma$ and $......... \pi$ bonds.

$(a)$ Discuss the concept of hybridization. What are its different types in a carbon atom.
$(b)$ What is the type of hybridization of carbon atoms marked with a star in the following structures:
$(a)$ $\overset{*}{C}H_2 = CH - C(=O)OH$
$(b)$ $CH_3 - \overset{*}{C}H_2 - OH$
$(c)$ $CH_3 - CH_2 - \overset{*}{C}H = O$
$(d)$ $\overset{*}{C}H_3 - CH = CH - CH_3$
$(e)$ $CH_3 - \overset{*}{C} \equiv CH$