Hybridization of $1$ and $2$ carbon atoms in $\mathop {CH_2}\limits^1 = \mathop C\limits^2 = CH_2$

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

Which among the following possesses a $sp$ carbon in its structure?

$(a)$ 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:
$(a)$ $\overset{*}{C}H_2 = CH - C(=O)OH$
$(b)$ $CH_3 - \overset{*}{C}H_2 - OH$
$(c)$ $CH_3 - CH_2 - \overset{*}{C}H = O$
$(d)$ $\overset{*}{C}H_3 - CH = CH - CH_3$
$(e)$ $CH_3 - \overset{*}{C} \equiv CH$

Examine the following common chemical structures to which simple functional groups are often attached. Which of these systems have essentially planar geometry?

Which of the following compounds contains carbon atoms with more than one type of hybridization?