Which of the following substances is least able to cross the blood-brain barrier a

James Weather and Climate variable gases (2% by volume) aka greenhouse gases -water vapor (the most variable gas [0-4% by volume; 0 = deserts, 4 = rainforests]) -methane (CH4) -ozone (O3) -aerosols/particulates -carbon dioxide (CO2) -nitrous oxide (N2O) -CFCs where to find water vapor -closer to 0%: Death Valley (hot desert) vs. cold air does not allow much moisture to exist -a source of energy in the atmosphere (excess amount of moisture) -one of the most important greenhouse gases carbon dioxide -also a very important greenhouse gas -causes warming methane -by product of decomposition (animals, humans, etc.) ozone -ozone/pollution alerts -3 chemicals bonded oxygen atoms (not a very stable compound) -does different things at different places in the atmosphere -blocks incoming UV radiation from the sun in the upper level ("good ozone") -form of pollution when we have stagnant weather patterns ("bad ozone") = by product of human activities >> gas fumes coming into contact with solar radiation atmospheric origins -particles in solar winds formed Earth -earth cooled -outgassing (including water vapor) -clouds formed >> rain fell -at first rain "boiled" away -after cooling, oceans filled with water *nitrogen + hydrogen >> nitrogen + oxygen formation of oxygen -first atmosphere contained little amounts of oxygen (how did the oxygen, as we know it today, form) -UV radiation through chemical reactions produced some oxygen -largely though, most came through photosynthesis (from bacteria first plants later as Earth "matured")