Question

An experiment was constructed to determine the source of $C,H$ and $O$ during photosynthesis process by plants in which plants were grown in a variety of radioactive compounds and a Geiger counter was used to determine whether the starch produced by the plants was radioactive.
Molecule Radioactive Starch
Expt. 1 ${}^{14}{C}_2$ $+$
Expt. 2 $H_2^{18}O$ $-$
Expt. 3 $C^{18}{O}_2$ $+$
Which of the following is a source of oxygen?

• A. $C{O}_2$
• B. $H_{2}O$
• C. $O_2$
• D. None of the above
• E. All of the above

Answer 1

The correct option is B $H_{2}O$

When the hydrogen in water was radioactive, the starch produced by plants were not. This shows that the hydrogen or oxygen from plants were not used for the release of oxygen. Hence the source of oxygen is water. The correct answer is option B.