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When the balloon is rubbed on the sweater again, and the blue negative charges are collected, and then brought close to the wall, they will still move towards the positive charges on the wall. This is because opposite charges attract each other.
Positive charges attract negative charges, and negative charges attract positive charges. Since the wall has positive charges, the negative charges on the balloon are attracted to the wall. On the other hand, the positive charges on the wall are not attracted to the balloon because like charges repel each other.