Question

the equation for photosynthesis is ( 6h_2o ) (water) ( +6co_2 ) (carbon dioxide) + light energy ( \to c_6h_{12}o_6 ) (glucose) ( +6o_2 ) (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.

Explanation:

To determine how scientists traced the oxygen path in photosynthesis:

1. Isotope Type: Scientists used a stable isotope (e.g., \(^{18}\text{O}\)) for tracing oxygen in photosynthesis, as radioactive isotopes were not the primary method here.
2. Detection Tool: A Becquerel counter is not used for stable isotopes. Wait, correction: Actually, in the classic experiment (e.g., using \(^{18}\text{O}\), a stable isotope), the tracking involved analyzing the isotope’s presence, but the options here have a mix. Wait, the correct approach: In the experiment to trace oxygen in photosynthesis, scientists used a stable isotope (like \(^{18}\text{O}\)) and tracked it (not with a Geiger counter, as Geiger counters detect radioactivity). Wait, the options: Let's re-express.

Wait, the key points:

• Stable isotopes (non - radioactive) are used for tracing in such classic photosynthesis experiments (e.g., the \(^{18}\text{O}\) experiment by Ruben and Kamen, but actually, the correct method here: the options given. Wait, the first two options use radioactive isotopes, but photosynthesis oxygen - tracing used stable isotopes. Geiger counters detect radioactivity, so they can't detect stable isotopes. Becquerel counter is also for radioactivity? Wait, no. Wait, the correct answer: They used a stable isotope and tracked it (the tracking method here: the options. Wait, the correct option is "They used a stable isotope and tracked it with a Becquerel counter." No, wait, no. Wait, the Geiger counter detects ionizing radiation (radioactive decay), so stable isotopes (no radioactivity) can't be detected by Geiger or Becquerel counters. But among the options, the only one that makes sense in terms of the experiment (using stable isotopes, like \(^{18}\text{O}\)) and the counter: Wait, maybe the question has a mix, but the correct answer is "They used a stable isotope and tracked it with a Becquerel counter." No, wait, no. Wait, the classic experiment used \(^{18}\text{O}\) (stable isotope) and the detection was done by mass spectrometry, but among the given options, the best fit is: They used a stable isotope and tracked it with a Becquerel counter? No, that's wrong. Wait, no, the first two options use radioactive isotopes, but the oxygen - tracing in photosynthesis used stable isotopes. Geiger counters detect radioactivity, so stable isotopes can't be detected by Geiger counters. So the only option with stable isotope and a counter (even if the counter is mis - named) is "They used a stable isotope and tracked it with a Becquerel counter." But actually, the correct experimental method used stable isotopes and mass spectrometry, but among the options, the answer is: They used a stable isotope and tracked it with a Becquerel counter. Wait, no, let's re - evaluate.

Wait, the options:

1. Radioactive isotope + Becquerel counter: Radioactive isotopes emit radiation, Becquerel counter measures radioactivity. But photosynthesis oxygen tracing used stable isotopes.

1. Radioactive isotope + Geiger counter: Geiger counter measures radioactivity, but again, stable isotopes were used.

1. Stable isotope + Becquerel counter: Stable isotopes don't emit radiation, but maybe the question's "Becquerel counter" is a misnomer, and this is the best option among the given ones.

1. Stable isotope + Geiger counter: Geiger counter can't detect stable isotopes (no radioactivity), so this is wrong.

So the correct option is "They used a stable isotope and tracked it with a Becquerel counter."

Answer:

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