Why does the balloon stick to the wall?
A balloon can stick to a wall due to static electricity. When you rub a balloon on your hair or on a woolen fabric, electrons are transferred from one material to the other. This typically happens because different materials have different tendencies to gain or lose electrons.
For instance, when you rub a balloon on your hair, the balloon tends to take some of the electrons from your hair, leaving your hair positively charged and the balloon negatively charged. This separation of charge creates a static electrical condition.
When you then bring the negatively charged balloon near a wall, the negatively charged balloon induces a positive charge on the wall's surface due to electrostatic induction. Though the wall is generally electrically neutral, the charges in the atoms and molecules of the wall's surface can shift slightly, with positive charges moving closer to the balloon and negative charges being repelled.
The attraction between the positively charged surface and the negatively charged balloon can be strong enough to overcome the force of gravity, causing the balloon to stick to the wall. The sticking effect will last until the charges on the balloon and the wall dissipate or redistribute, which might occur after a short period of time due to charge leakage through the air or onto the surfaces around.