Answer:
Density of iron is higher than the density of oxygen because iron is solid and the particles in it are very compact but oxygen is not dense as it is gas and particles in it are loosely packed.
It might be radiation and reflection but I’m not sure
A sedentary lifestyle is when you don't make any exercise. For example, if I spent a whole week just sitting down answering questions, that would be an example of a sedentary lifestyle, because I'm not running or jogging. Having that type of lifestyle can make you fat and get health problems.
Have a nice day! :)