When the negatively charged balloon is brought near the neutral wall, it induces a charge separation within the wall due to electrostatic induction. The negative charges in the wall (electrons) will be repelled by the negatively charged balloon, causing them to move away from the side of the wall that is closest to the balloon. As a result, the side of the wall nearest to the balloon will acquire a positive charge because the electrons have moved away, leaving behind a deficit of negative charge.
In summary, when the negatively charged balloon is brought near the neutral wall, the side of the wall closest to the balloon will become positively charged, while the side furthest away will remain neutral. This creates a polarized effect in the wall, with one side being positive and the other side remaining neutral.