The number of protons in the nucleus of an atom is its atomic number (Z). This is the defining trait of an element: Its value determines the identity of the atom. For example, any atom that contains six protons is the element carbon and has the atomic number 6, regardless of how many neutrons or electrons it may have.
In low light no plants grow. With no plants no animals can eat so less animals remain or stay there. With less animals less animals respire and breathe out CO2.
You would expect a plant to produce more oxygen on a sunny day because there are more sun rays available to plants so photosynthesis is easier to maintain, as well as oxygen production.
