What will be minimum insulation resistance of a system operated at maximum voltage of 250V?

Correct option is A

​$$\begin{array}{|c|c|}\hline\textbf{Maximum voltage rating of equipment} & \textbf{Minimum I.R. value} \\\hline250 \text{ volts} & 25 \text{ M} \Omega \\\hline600 \text{ volts} & 100 \text{ M} \Omega \\\hline5 \text{ kV} & 1000 \text{ M} \Omega \\\hline8 \text{ kV} & 2000 \text{ M} \Omega \\\hline15 \text{ kV} & 5000 \text{ M} \Omega \\\hline25 \text{ kV} & 20,000 \text{ M} \Omega \\\hline35 \text{ kV} & 100,000 \text{ M} \Omega \\\hline\end{array}$$​​