Naming of a molecule
As, your question isn't much clear and it needs to be focused little more.
From current state of this question, I can provide you the answers for specific questions that I get to understand from its current state.

$\ce{H_2 \ \ C=C=O}$
What is the group of the  molecule?

Well this is known as ketene.

how to characterize it and how this is dissimilar to ketone?



Ketenes are generally very reactive, and participate in various cycloadditions. They will also undergo [2+2] cycloaddition reactions with electron-rich alkynes to form cyclobutenones, or carbonyl groups to form beta-lactones.



Ketones engage in many organic reactions. The most important reactions follow from the susceptibility of the carbonyl carbon toward nucleophilic addition and the tendency for the enolates to add to electrophiles.

See this and this

If we add $\ce{O2}$ with it then will we get $\ce{CO2}$?

No! I hope structure of ketene and wikipedia articles make it clear to you why. :)
Also see this.