What energy levels are core electrons in?

Air can be considered a mixture. which statement does not explain why?

Nuclear decay is the spontaneous decay of one element into a. an x-ray b. a ray of light c. another element

Which statement best describes isomers? a. isomers are alcohols that have the same functional group. b. isomers have at least one carbon-carbon double bond. c. isomers have the same molecular formula but different structural properties.