The statement that is not true about ozone is:

We have to identify which one of the four given statements about ozone $$\left(O_3\right)$$ is not correct. We shall examine every option one by one, recalling the relevant chemical facts and writing each accompanying reaction explicitly, so that every step is clear.

First we recall the universally accepted mechanism for the destruction of ozone by chlorofluorocarbons (CFCs). After the CFC molecule reaches the stratosphere, the high-energy ultraviolet radiation breaks the $$C-Cl$$ bond and releases a chlorine free radical $$\left(Cl^{\bullet}\right)$$. The key propagation step in the ozone-depletion cycle is

$$Cl^{\bullet + O_3 \;\longrightarrow\; ClO^{\bullet} + O_2}$$

and not the formation of molecular chlorine $$\left(Cl_2\right).$$ This fact will be needed when we test Option A.

Now we move through the options sequentially.

Option A: “in the stratosphere, CFCs release chlorine free radicals (Cl) which reacts with $$O_3$$ to give chlorine.”
According to the mechanism just written, the product of $$Cl^{\bullet}$$ reacting with $$O_3$$ is $$ClO^{\bullet}$$ (chlorine monoxide radical) along with $$O_2$$, not molecular chlorine $$\left(Cl_2\right).$$ So the wording “to give chlorine” is chemically wrong. Hence Option A is false.

Option B: “in the atmosphere, it is depleted by CFCs.”
We have just seen that CFC-derived $$Cl^{\bullet}$$ radicals destroy ozone. Therefore the statement that ozone is depleted by CFCs is scientifically correct. So Option B is true.

Option C: “in the stratosphere, it forms a protective shield against UV radiation.”
The stratospheric ozone layer indeed absorbs a large fraction of the harmful ultraviolet radiation coming from the Sun, thereby protecting living organisms on Earth. Consequently this statement is also true.

Option D: “It is a toxic gas and its reaction with NO gives $$NO_2$$.”
Ozone is indeed toxic at ground level, and the reaction between nitric oxide and ozone is well known:

$$NO + O_3 \;\longrightarrow\; NO_2 + O_2$$

Since the product $$NO_2$$ is correctly stated, Option D is true.

From the analysis, Options B, C, and D are all correct statements, while Option A is incorrect. We were asked to point out the statement that is not true, so Option A is the required choice.

Hence, the correct answer is Option A.