A balloon gets negatively charged by rubbing ceilings of a wall. Does this mean that the wall is positively charged? Why does the balloon eventually fall?
No, this does not imply that the wall is positively charged. The balloon induces a charge of opposite sign in the ceiling of the wall, causing the balloon and the ceiling to be attracted to each other. The balloon eventually falls because its charge slowly diminishes as it leaks to ground. Some of the charge on the balloon could also be lost due to the presence of positive ions in the surrounding atmosphere, which would tend to neutralise the negative charges on the balloon.