why charge not repulson outer surface of metal sheet

Dear student,

The question is not very clear in language. However assuming that it asks why charges are not repelled out of the outer surface of metal sheet, the answer is below-

The free electrons in the metal can freely move inside the conductor and repel as much as possible, they still cannot leave the metal surface even when they repel even in that state and hence reside on the surface.

Hope it helps.