Properties of Air

Air is a mixture of gases that surrounds the Earth. It is composed primarily of nitrogen (about 78%), oxygen (about 21%), and small amounts of other gases such as carbon dioxide, water vapor, and noble gases. Air has several properties that make it unique and essential for life on Earth. Among the given options, the true statement regarding the properties of air is option 'D': The composition of air varies from place to place.

1. Composition of Air Varies from Place to Place
The composition of air can vary slightly depending on the location. While the proportions of nitrogen and oxygen remain relatively constant, the presence of other gases can vary. For example, areas with high levels of pollution may have higher concentrations of carbon dioxide or other harmful gases. Additionally, the amount of water vapor in the air can vary depending on the humidity of the region. These variations in air composition can have significant effects on the quality of the air and the health of organisms in that particular area.

2. Air is Not a Good Conductor of Electricity
Contrary to option 'A', air is actually a poor conductor of electricity. It is an insulator, meaning it does not allow the flow of electric current easily. Unlike metals or other conductive materials, air does not have free electrons that can carry charge. However, if the voltage is high enough, air can become ionized and conduct electricity, leading to phenomena such as lightning. But in general, air is a poor conductor of electricity.

3. Air is a Poor Conductor of Heat
Option 'B' is also incorrect. Air is a poor conductor of heat. It is a good insulator, which means it does not transfer heat efficiently. This is why air is often used as an insulating material in buildings, as it helps to reduce heat transfer between the inside and outside environment. Additionally, air has low thermal conductivity, meaning it does not conduct heat well. This property is important for the regulation of temperature on Earth and the maintenance of suitable environments for living organisms.

4. Air is Translucent
Option 'C' is incorrect as well. Air is not translucent in nature. Translucency refers to the property of allowing light to pass through but scattering it in the process. Air, being a gas, is invisible to the naked eye. It is transparent, meaning it allows light to pass through it without significant scattering or absorption. This is why we can see clearly through the air.

In conclusion, the true statement regarding the properties of air is that its composition varies from place to place. The other statements, such as air being a good conductor of electricity, a good conductor of heat, or translucent, are incorrect.