What are some examples of endothermic reactions?

What are the first three quantum numbers for the electrons located in subshell 2s?

Stage in which a star’s outer layers have started to cool and grow outward?

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