Why durin the experiment"electrolysis of water" the oxygen fill the hole tube, when the hydrogen fil only half

Question

or maybe full of hydrogen and half full of oxygen i am confused

Answer 1

The chemical equation for electrolysis of water is:

2 H2O --> 2 H2(g) + O2(g)

So, you form twice as many moles of H2 as you do of O2. So, the oxygen tube will be only half filled,when the hydrogen side is filled.