The most important method of preparation of hydrocarbons of lower carbon number is

Pure methane can be prepared by

Which of the following has the highest knocking tendency in an internal combustion engine?

In the bromination of isobutane,the relative reactivity rates of $1^oH, 2^oH,$ and $3^oH$ are $1 : 82 : 1600$ respectively. Calculate the percentage yield of products $(a)$ and $(b)$ in the following reaction:
$CH_3-CH(CH_3)-CH_3 (excess) + Br_2 \xrightarrow{hv} (a) CH_3-C(Br)(CH_3)-CH_3 + (b) CH_3-CH(CH_3)-CH_2Br$

$A$ sample of $2,3-$dibromo$-3-$methylpentane is heated with zinc dust. The resulting product is isolated and then heated with $HI$ in the presence of red phosphorus. Indicate the structure that represents the final organic product formed in the reaction.

The major product obtained in the photo-catalyzed bromination of $2-$methylbutane is: