$(i)$ $\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}-CH_2} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,|}
\end{array}} \\
{C{H_3} - {C^ + }} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}}
\end{array}$
$(ii)$ $\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,|}
\end{array}} \\
{C{H_3} - {C^ + }} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{H}}
\end{array}$
$(iii)$ $\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,|}
\end{array}} \\
{C{H_3} - {C^ + }} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}}
\end{array}$
$(iv)$ $Ph - CH ^{+}-\underline{ CH }_{3}$
Carbocation $(i)$ shows eight hyperconjugation structures.
Carbocation $(ii)$ shows six hyperconjugation structures.
Carbocation $(iii)$ shows nine hyperconjugation structures.
Carbocation $(iv)$ shows $+M$ effect.
Therefore, the correct stability order is : $iv > iii > i > ii$