Question

Which one is not one of the most common elements of organic compounds?
A. Hydrogen
B. Helium
C. Nitrogen
D. Phosphorus

Answer 1

B. Helium without any doubt. :)

Answer 2

I believe the correct answer among the choices listed above is option B. Helium is the substance that is not one of the most common elements of organic compounds. The most common element would be carbon, hydrogen, nitrogen and phosphorus.