Which of the following will have the least hindered rotation about the carbon-carbon bond?

Aluminium carbide on reacting with water gives

An alkane $(Y)$ requires $8$ moles of oxygen for complete combustion and on chlorination with $Cl_2/h\nu$, $(Y)$ gives only one monochlorinated product $(Z)$. The total number of primary carbon atoms in $(Y)$ is . . . . . . .

$Br^{\bullet}$ will abstract which of the hydrogen most readily?

Photochemical chlorination of alkane is initiated by a process of

$Ph^{-}MgCl \xrightarrow{\text{Hydrolysis}} \text{Product}$
Product will be