Question

If green plant cells are incubated with ${O^{18}}$- labeled water, which of the following will become radioactive when the cells are exposed to light.
A. Oxygen
B. Carbon dioxide
C. Water
D. Sugar

Answer 1

Hint: Green plant cells become incubated when heavy oxygen combines with them. Heavy oxygen plays a vital role in the study of the process which is known as photosynthesis. Here, we are going to find the elements which become radioactive when they are exposed to light. Through this, it can be found and analyzed.

Complete answer:
Samuel Ruben and Martin Kamen in the year 1941 found the liberation of oxygen during the process of photosynthesis that comes under water. This was found by them while working with the chlorella which is known as unicellular green alga. Heavy oxygen once evolved becomes natural and also becomes the stable isotope of oxygen. The following are some of the cases to find the radioactive element. They are as follows:
> When the normal water and the radioactive carbon dioxide were used, then normal oxygen evolved. Radioactive carbon dioxide is also denoted as $C{O_2}^{18}$.
> When the normal carbon dioxide and radioactive water were used, then radioactive oxygen evolved. Radioactive water is also denoted as ${H_2}{O^{18}}$.
> When the heavy oxygen is being incubated, they become radioactive only with the oxygen when exposed to light. So here in both of the cases we could see that oxygen is evolved.

Hence, the correct answer is Option A.

Note:
 Radioactive substances are mainly formed by the heavy oxygen. These are one of the environmental isotopes. This is the important precursor. They are used in the emission tomography. Oxygen having the mass number of 18 is mainly considered as the heavy oxygen. Heavy oxygen becomes radioactive only when the evolution of the oxygen occurs.