Which gas is lighter than air and can be explosive when mixed with oxygen?

The correct gas that is lighter than air and can be explosive when mixed with oxygen is hydrogen. Hydrogen is the lightest element on the periodic table and has a lower density than air, which means it rises quickly when released in the atmosphere. When mixed with oxygen, hydrogen can form a highly combustible mixture, and under the right conditions, it can ignite and cause an explosion.

This explosive potential is also relevant for various industrial processes, where safety measures must be taken to avoid creating flammable environments. While other gases like propane, acetylene, and methane have their own risks and flammability characteristics, hydrogen is distinct in its extreme lightness and high explosiveness in the presence of oxygen.