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

In the preparation of alkanes,a concentrated aqueous solution of sodium or potassium salts of saturated carboxylic acids is subjected to:

Identify the correct statements from the following:
$(i)$ Petrol and $CNG$ operated automobiles cause less pollution.
$(ii)$ Alkanes having tertiary hydrogen can be oxidised to alcohols by $KMnO_4$.
$(iii)$ Methane can be prepared by Kolbe's electrolytic method.
$(iv)$ Alkyl chloride on reduction with zinc and dilute hydrochloric acid gives alkane.

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 . . . . . . .

Identify all the possible monochloro structural isomers expected to be formed on free radical monochlorination of $(CH_3)_2CHCH_2CH_3$.

The general formulas for alkene and alkane are respectively: