It may not be safe because of the harmful chemicals that are in it and also because of how much it is holding or consumes.
No, methane is not safe to breathe as it can displace oxygen in the air, leading to suffocation.
Yes
It is ceartainly safe to breathe, assuming that the rest is normal air.
They will have no air to breathe
Well, some air you breathe comes from car exhaust, factories, etc.
It is safe to breathe through the mouth, but it is a tiny, tiny bit better to breathe through the nose.If you breathe through the nose, the air has to travel longer before it reaches the lungs. And that longer joúrney means that any dust in the air has had a better chance of getting caught on the inner surface of the airways, the air will be closer to body temperature, and if the air is dry, it'll have picked up some moisture along the way as well too. Not actually required, but things that'll make life easier on the lungs.
Nothing much. Exhaled air has about 4% less oxygen in it compared to regular air, but it's still perfectly safe, if a bit smelly, to breathe.
might be safe but unconfortabel
Well, the air in China is mostly not safe to breathe in, since the air is full of PM 2.5 particles which are unhealthy for your body. To make things worse, only 3 cities out of 73 passed air quality standards, which means wherever you go you will most likely see smog in the sky.
You could use an air purifier with a HEPA filter to remove dust particles from the air, making it safe to breathe. Additionally, regularly cleaning and dusting the room, using an air humidifier to trap dust particles, and ensuring good ventilation can help improve air quality.
They breathe air with lungs.
They do breathe air.