Which of the listed substances are simple and which are complex: a) carbon dioxide; b) salt; c) copper; d) hydrogen;

Which of the listed substances are simple and which are complex: a) carbon dioxide; b) salt; c) copper; d) hydrogen; e) aluminum; f) marble? What is the difference between these groups of substances?

Simple substances:
c) copper
d) hydrogen
e) aluminum
Complex substances:
a) carbon dioxide
b) salt
f) marble

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