During thunderstorms, when the magnitude of the accumulated charges becomes very large, the air which is normally a good conductor of electricity is able to resist their flow.

The given statement is false.

During thunderstorms, when the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.