In psychology which is the field that studies human behavior and development, there are different branches that deal with different aspects. This includes the sports psychology that focuses on understanding the psychological factors that influence sports performance; forensic psychology that is applied in the justice system to determine insanity, child custody, reliability of testimonies, etc.; developmental psychology that focuses on the evolution of individuals during their life and psycholinguistic that deals with the development of language and all factors related to it including those that might make an individual has issues to express himself. This implies someone with a speech impediment needs to visit a psycholinguistic because this is the type of psychologist that focuses on the development of language and therefore the most suitable to help or support this individual.
Natural selection is when the organisms that have the better adaptation so they survive. In this case, the green was the better adaptation so they lived.
Well, nitrogen is the gas that makes up 78% of the earth's atmosphere.
I would guess its in the air that we breathe. I am not really sure. Just basing this answer off of research.