Final answer:
A balloon sticks to a wall due to the static charge it accumulates when rubbed against wool, which causes electrostatic attraction between the balloon and the wall.
Step-by-step explanation:
When a balloon is rubbed against woolen clothes, it picks up extra electrons, resulting in a negative static charge. When this negatively charged balloon is brought close to a wall, it induces a positive charge on the surface of the wall. The attraction between the negative charge on the balloon and the induced positive charge on the wall causes the balloon to stick to the wall. This is a result of electrostatic forces and is similar to how static electricity can make hair stand up or clothes stick together straight out of the dryer.