As I googled and found out that the O2 molecule size is 120 pm. At one point Ant-man goes subatomic, that is, smaller in size than the original O2 molecule size. And my question arises. How was Ant-man able to breath when he goes sub-atomic? It wouldn't fit in his lungs. Hope some one will put some light on the mystery.
SCUBA. Or in this case, Self Contained Microcosm Breathing Aparatus.
In an interview featured in the [July 2015] issue of Empire, costume designers Sammy Sheldon and Ivo Coveney discuss the loosely-based logistics behind the Ant-Man suit worn by Rudd’s Scott Lang. Adhering to realism in one sense, the suit is designed to be self-contained, since oxygen molecules would be too large to breathe for a shrunken superhero. ... The team of Sheldon and Coveney, who openly made this supposed style-over-substance design choice, have been on board the Peyton Reed-directed Ant-Man project since the days it still called Edgar Wright its skipper.
One such area that Marvel have addressed is the notion of oxygen absorption. In a recent interview with Empire, Ant-Man's costume designers, Sammy Sheldon and Ivo Coveney, revealed one of the scientific limitations that they had placed upon Paul Rudd's characters. "When you shrink, the molecules in the air are too big for your lungs," explained Sheldon. "He has to be fully contained or he'd die."
In essence, the suit shrinks everything Ant-Man needs to be able to survive. Regardless of the quantum effects they state happen at the subatomic levels, we know Scott was only subatomic for minutes real time. And we don't know how small the O2 particles are made in the suit's oxygen tank, but considering the power of pym-particles, they can be incredibly compact. He could have a near unlimited amount of air.
Note: Scott Always has his helmet on when shrunken. Always. Not one scene has Scott, Hank, Janet, or even Cross shrink without the helmet on and in place.
In the end though, the technical accuracy, like in most comics and movies, takes a back seat to the rule of cool:
We had a long discussion about the two cables going into his helmet. They're a massive weakness - Yellowjacket could just rip them off and he's dead. But, in the end, it just looks cooler with them on.