Explanation:
+I effect increases stability of carbocation. In (i), +I effect of CH3 - O is greater than - CH3, Hence, $\text{CH}_3-\text{O}-\text{CH}_2^\oplus$ is more stable than $\text{CH}_3-\text{CH}_2^\oplus.$
In (iii), $\text{CH}_2=\text{CH}-\text{CH}_2^\oplus\leftrightarrow\ ^\oplus\text{CH}_2-\text{CH}=\text{CH}_2$ is stabilized by resonance effect. While $\text{CH}_3-\text{CH}_2-\text{CH}_2^\oplus$ is stabilized by +I effect $-\text{C}_2\text{H}_5$ group. Resonance effect is stronger than +1 effect. Hence, $\text{CH}_2=\text{CH}-\text{CH}_2^\oplus$ is more stable than $\text{CH}_3-\text{CH}_2-\text{CH}_2^\oplus$.
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$\begin{array}{*{20}{c}}
{C{H_2} = CHC{H_2}CHC{H_3} + KOH\xrightarrow[{heat}]{{{\text{alcohol}}}}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{Br\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}$