The hydrocarbon $(X)$ with molar mass $80 \ g \ mol^{-1}$ and $90 \%$ carbon has $............$ degree of unsaturation.

What is the correct order of acidity for the following hydrocarbons?

How many cyclic structures are possible for $C_4H_6$?

"$P$" is a hydrocarbon with the molecular formula $C_8H_{14}$. On ozonolysis,"$P$" forms "$Q$". "$Q$" on treatment with alkali under reflux conditions produces "$R$",which on treatment with $I_2/NaOH$ gives a yellow precipitate. Acidification of the solution gives "$S$". The structure of "$S$" is given below:
(Structure $S$: $1-$methyl$-2-$oxocyclopentanecarboxylic acid derivative or similar cyclic structure as per common reaction pathways).
The correct structure of "$P$" is:

Styrene on reaction with reagent $X$ gave $Y$, which on hydrolysis followed by oxidation gave $Z$. $Z$ gives a positive $2,4-DNP$ test but does not give the iodoform test. What are $X$ and $Z$ respectively?

The octane number is associated with which petroleum product?