Correct Answer - Option 2 : 0.9149 p.u

\(\begin{array}{l}
{X_{new}} = {X_{old}} \times \left( {\frac{{MV{A_{new}}}}{{MV{A_{old}}}}} \right) \times {\left( {\frac{{k{V_{old}}}}{{k{V_{new}}}}} \right)^2}\\
{X_{new}} = 0.5 \times \left( {\frac{{50}}{{25}}} \right) \times {\left( {\frac{{13.2}}{{13.8}}} \right)^2} = 0.9149\;p.u.
\end{array}\)