a
(a) We know that greater the number of alkyl groups attached to double bonded carbon atoms, more stable is the alkene. Therefore most stable is \({R_2}C = C{R_2}\)

\(\begin{matrix}
   ^{R}  \\
   _{R}  \\
\end{matrix}\begin{matrix}
   \backslash   \\
   /  \\
\end{matrix}C=C\begin{matrix}
   /  \\
   \backslash   \\
\end{matrix}_{R}^{R}\)