For which of the following reactions is Markovnikov's rule most applicable?

Addition of bromine to $1, 3-$butadiene gives

Baeyer's reagent is used for the detection of

Select the suitable reagent for the conversion shown below:

Ozonolysis of an alkene produces only one dicarbonyl compound. The structure of the alkene is:

An organic compound $X$ with molecular formula $C_{11}H_{14}$ gives an optically active compound on hydrogenation. Upon ozonolysis,$X$ produces a mixture of compounds $P$ and $Q$. Compound $P$ gives a yellow precipitate when treated with $I_{2}$ and $NaOH$ but does not reduce Tollen's reagent. Compound $Q$ does not give any yellow precipitate with $I_{2}$ and $NaOH$ but gives Fehling's test. The compound $X$ is: