Oxygen gas is a very reactive element. Oxygen gas is the most abundant element on Earth. Oxygen is part of very many natural compounds, in minerals as in organic material and of course in water, H2O. Combustion usually is a reaction of a material with oxygen. Elemental oxygen in the form of O2 is to 21% part of our air and it is used by humans and animals for respiration. Oxygen gas is also produced by plants doing photosynthesis, most of it by algae in the sea and by forests on land. O3 instead is ozone, a poisonous gas, which in a high atmospheric layer blocks otherwise deadly UV rays from the Sun. In the right picture is showed the ionized Oxygen gas. That is possible when the Oxygen gas is rarefied (or in low pressure atmosphere), using a high voltage transformer or simply using a Tesla Bulb for sale here.