Electrolysis
Electrolysis is using electricity to break water apart into hydrogen gas and oxygen gas.
Think of it this way
Water in a pot is made of tiny pairs — one hydrogen piece bonded to one oxygen piece. When you run electricity through the water, it acts like a wedge that pries those pairs apart. The hydrogen pieces float up to one side and collect as bubbles. The oxygen pieces collect on the other side, each type going to its own spot.
Explaining electrolysis by grade level
When you put two pencils in salt water and connect them to a battery, something happens. Tiny bubbles start forming on each pencil. The electricity from the battery is pulling water apart into two invisible gases. One pencil gets bubbles of hydrogen. The other gets bubbles of oxygen. The water is splitting right in front of you.