Question

Assertion :The $O_2$ given out during photosynthesis in plants involves O-atoms of $H_{2}O$ and not of $C{O}_2$. Reason: $C{O}_2^{18}+H_{2}O⟶Starch+{}^{18}{\text{O}}_2$

• A. $S$ is correct but $E$ is wrong
• B. $S$ is wrong but $E$ is correct
• C. Both $S$ and $E$ are correct and $E$ is correct explanation of $S$
• D. Both $S$ and $E$ are correct but $E$ is not correct explanation of $S$

Answer 1

The correct option is A $S$ is correct but $E$ is wrong

From the radioactive tracer technique, following is established.

${\text{CO}}_2+{\text{H}}_2{}^{18}\text{O}⟶({\text{C}}_6{\text{H}}_{10}{\text{O}}_5{)}_n{+}^{18}{\text{O}}_2$

Thus, when water contains labelled oxygen, the oxygen gas obtained after photosynthesis also contains labelled oxygen. So, the oxygen given out during photosynthesis in plants involves O-atoms of water and not carbon dioxide.

Hence, the assertion is correct but the reason is not correct.