Bubbling Magnesium

When magnesium ribbon is placed in hydrochloric acid, hydrogen gas is produced causing the mixture to bubble.
Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

If they hydrogen gas is collected, it can be ignited to demonstrate the potential safety concerns of an evolved gas.
H2 (g) + O2 (g) → H2O (g)

Igniting Magnesium

burning magnesium

When magnesium is ignited, it is readily oxidized by oxygen in the air producing an incredibly bright light and intense heat.
2Mg (s) + O2 (g) → 2MgO (s)

Hydrogen Balloons

hydrogen balloon explosion

This demo shows the explosiveness of hydrogen, by igniting a balloon filled with hydrogen.
2H2 (g) + O2 → 2H2O (g)