Answer:
the main answer is carbon although its really carbon, hydrogen, and oxygen
to remember each macromolecule, you can use this reference...
Carbohydrates = CHO (carbon, hydrogen, oxygen)
Lipids = CHO (carbon, hydrogen, oxygen)
Proteins = CHON (carbon, hydrogen, oxygen, nitrogen)
Nucleic Acids = CHONP (carbon, hydrogen, oxygen, nitrogen, phosphorus)
hope this helped :)