Which federal state is Berlin?

EDITORIAL LEARNING AID

Why is this answer correct?

On the map in the questionnaire, Berlin is marked with the number 4. Berlin lies in the east of Germany and is completely surrounded by the state of Brandenburg. The other numbers designate other federal states.

Berlin lies in the middle of Brandenburg: number 4.

This translation and explanation are editorial learning aids. The official German wording and answer key govern the examination.