What is the state of aggregation (gas, liquid) of oxygen in blood?

Atmospheric oxygen is in O2 and a gas. Then we inhale the air, our efficient lungs do the magic to filter out the oxygen and *push* them into the blood stream.


When we say hemo and globin transport the oxygen using the iron ions. In what state oxygen is transported in the blood? as a gas or a liquid or an ion? It is hard for me to conceive of the idea that oxygen would be in gaseous form in the blood. "GAS in blood?" e.g. *Arterial Blood Gas Test*


Also, how does the lungs *convert* the gas into *something* that is compatible to be in blood?


References:
[Amount of Oxygen in the Blood](http://courses.washington.edu/conj/resp/oxygen.htm)




Regarding the state of oxygen in blood: It is in solution in the blood plasma (which mostly consists of water), in the form of single molecules. Think of water which you leave exposed to air: carbon dioxide will be captured and dissolved (along with the other gases in air), but these molecules are not gaseous or liquid, but rather "in solution", which is different from the "classical" states.


Back to oxygen: As your reference already states, most of the oxygen in solution will bind to hemoglobin. The actual state of oxygen in that complex has been debated, but it is believed to be reduced by the hemoglobin iron to the superoxide anion, coordinated to Fe$^{3+}$. See [Wikipedia](https://en.wikipedia.org/wiki/Hemoglobin#Iron.27s_oxidation_state_in_oxyhemoglobin) on this.


Also, the lungs do not "convert" the atmospheric oxygen to anything, they rather allow, due to their very large surface area, the quick exchange of oxygen/carbon dioxide in solution and in the air.


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We inhale a lot of other atmospheric gases with oxygen. The mixture of gases go to the sacs in our lungs which is crawling with lots of blood capillaries.  

The blood (specifically RBCs) contains a pigmented substance called haemoglobin, each of them can bind 4 oxygen molecules (if working normally) forming a substance named Oxyhaemoglobin.  

This is then carried through blood vessels to the cells in the body. 


The binding phenomena of oxygen with haemoglobin is reversible in nature. That is, at high oxygen concentration oxygen binds with haemoglobin to form oxyhaemoglobin, but when the oxygen concentration decreases (in cells, which are in need of oxygen) the oxygen again dissociates from haemoglobin. 


The overview thus provided here, if you wish to be more specific about chemical reactions you may find [this](http://www.rsc.org/Education/Teachers/Resources/cfb/transport.htm) useful.


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