When calculating by dimensional analysis, which part of the conversion ratio should you complete in your first step?

Which of the following describes a compound? (hint: carbon and oxygen bo a. a piece of pure carbon, containing only carbon atoms b. oxygen gas surrounding a solid piece of carbon c. a substance made of two oxygen atoms for each carbon atom carbon and oxygen atoms mixed without being bonded together

Answer asap : ( a. how does mucus prevent the entry of pathogens? b. describe two ways white blood cells protect us from pathogens.

The molecular weight of carbon dioxide, co2, is 44.00 amu, and the molecular weight of nitrous dioxide, no2, is 46.01 amu, so no2 diffuses co2