Which of the following compounds do not have $sp^3$ carbon atom$(s)$?
$I$. Acetone
$II$. Acetic acid
$III$. Buta-$1,3$-diene
$IV$. Propyne
$V$. Naphthalene

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

The enolic form of acetone contains

In the compound $CH_2 = CH - CH_2 - CH_2 - C \equiv CH$,the $C_2 - C_3$ bond is of the type

What is the number of $sp^3$ hybridized carbon atoms in $HO(CH_2)_2CH(CH_3)_2$?

Consider a positively charged $C_2H_3$ species in which the positively charged carbon is $sp$-hybridized,the uncharged carbon is $sp^2$-hybridized and an empty $p$-orbital is perpendicular to the $\pi$ system. What is the best description of this cation?