$A$ hydrocarbon containing $2$ carbon atoms gives Sabatier and Senderen's reaction but does not give a precipitate with ammoniacal silver nitrate solution. The hydrocarbon is:

What is the major product expected from the following reaction?

Product $(A)$ is

$CH_3-CH=CH_2$ $\xrightarrow{Br_2, hv (\text{low conc.})} \dots$ $\xrightarrow{Mg, \text{Dry ether}} \dots$ $\xrightarrow{CH_3-CO-CH_3, NH_4Cl} \dots$ $\xrightarrow{H^{+}, \Delta} (X)$. The end product $(X)$ of the above reaction is:

Aqueous solution of sodium salt of $2-$methylbutanedioic acid on Kolbe's electrolysis gives:

An optically active alkene having molecular formula $C_8H_{16}$ gives acetone as one of the products on ozonolysis. The structure of the alkene is: