What is the purpose of the biogeochemical cycles?
to cycle energy through a food chain
to recycle matter through the biosphere
to recycle rocks through the layers of Earth
to cycle nutrients through the human body

correct answer is a. and d.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds