Explanation:

Ozone (O3) is a gas that is present in the Earth's atmosphere. It is formed when oxygen molecules (O2) are exposed to ultraviolet (UV) radiation from the sun. Ozone is an important component of the atmosphere as it helps to absorb and block harmful UV radiation from reaching the Earth's surface.

Detecting Ozone:

There are several methods that can be used to detect the presence of ozone in the atmosphere. These methods typically involve the use of chemicals that react with ozone to produce a visible color change. In this question, the correct answer is option 'C' (Mercury). Let's understand why:

Mercury:

Mercury is commonly used in ozone detection methods because it reacts with ozone to produce a characteristic blue color. This reaction is known as the Mercury Ozone Reaction and is widely used in ozone monitoring instruments such as ozone analyzers and monitors.

When ozone comes into contact with a mercury film or mercury vapor, it reacts to form mercuric oxide (HgO), which is a blue-colored compound. This blue color is easily detectable and provides a visual indication of the presence of ozone.

Other Options:

Option 'A' (Silver) and option 'B' (Sodium) are incorrect because although these elements can react with ozone, they do not produce a visible color change. Silver and sodium are sometimes used in detecting ozone, but they require additional chemical reactions or processes to produce a detectable signal.

Option 'D' (None of these) is incorrect because as mentioned above, mercury is indeed used to detect ozone in the atmosphere.

In Summary:

Ozone can be detected by using mercury, as it reacts with ozone to produce a visible blue color. This characteristic color change is utilized in ozone detection methods and instruments. Other elements such as silver and sodium can also react with ozone, but they do not produce a visible color change. Therefore, the correct answer to this question is option 'C' (Mercury).