Is there any place on Stack Exchange to ask science related questions ,
E = MC2, what does it really mean?
We know that oxygen is needed for various life forms; why are other gases like CO2 and nitrogen not?
"Science" is simply too broad of a field. There are many different types of science fields, and many different stack exchange sites that all fit into the scope of "science".
Here is a (non-inclusive) list of some sites that all represent [mostly or entirely] "science" questions: