2. Injection-based Volcano - This toy requires the user to fill a cup with baking soda and place it in a volcano pit. The injector is filled with vinegar and connected to the baking soda container. When the kid injects vinegar at varying speeds, the reaction can be observed as the volcano erupts. This toy is based on the principle of acids and bases reacting to release heat and carbon dioxide. The construction cost would be about $5-6, including a small quantity of baking soda and vinegar. However, this toy is relatively less durable due to the nature of reactions. I thought of this idea because it's based on a science experiment that first got me interested in chemistry and chemical reactions. It's engaging for young kids to see "explosions" and other compelling reactions to understand the underlying science.