Identify $A$ in the given chemical reaction.

In which of the following is the rotation around the carbon-carbon bond least restricted?

What is the minimum quantity (in grams) of methyl iodide required for preparing one mole of ethane by Wurtz reaction?
(Atomic weight of iodine $= 127$)

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

Methane and ethane both can be obtained in a single step from

$A$ molecule which has $1^{\circ}$,$2^{\circ}$ and $3^{\circ}$ carbon atoms is