Question

The equation for photosynthesis is 6H2O (water) + 6CO2 (carbon dioxide) + Light Energy → C6H12O6 (glucose) + 6O2 (oxygen). When first discovered, scientists were trying to decide if the oxygen in the product came from carbon dioxide or water. Which statement describes how scientists traced the path of oxygen?

They used a radioactive isotope and tracked it with a Becquerel counter.
They used a radioactive isotope and tracked it with a Geiger counter.
They used a stable isotope and tracked it with a Becquerel counter.
They used a stable isotope and tracked it with a Geiger counter.

Answer 1

None of the four is correct. Ruben and Kamen used the stable isotope oxygen-18 (18O) to label water and then detected 18O in the O2 produced using mass spectrometry — not with a Geiger or Becquerel counter (those detect radioactivity).