Answer:

Carbon dioxide (CO2) is the gas that is opaque to the outgoing terrestrial radiation. This means that it absorbs and traps heat energy emitted by the Earth's surface, preventing it from escaping into space. This phenomenon is known as the greenhouse effect, which plays a significant role in regulating the Earth's temperature and maintaining a habitable environment.

Explanation:

The Greenhouse Effect:
The Earth's atmosphere is composed of various gases, including carbon dioxide, nitrogen, oxygen, and others. When sunlight reaches the Earth's surface, it warms the surface, which then radiates heat energy back into the atmosphere. Some of this heat energy is absorbed by certain gases in the atmosphere, such as carbon dioxide, while others are reflected back into space.

Greenhouse Gases:
Certain gases, including carbon dioxide, methane, and water vapor, are known as greenhouse gases. These gases can absorb and emit infrared radiation, which is a form of heat energy. When solar radiation reaches the Earth's surface, it is absorbed and re-emitted as infrared radiation. Greenhouse gases in the atmosphere trap a portion of this infrared radiation, preventing it from escaping into space and thereby warming the Earth's surface.

Carbon Dioxide:
Carbon dioxide is one of the most significant greenhouse gases in the Earth's atmosphere. It is produced by natural processes such as respiration and volcanic activity, as well as human activities like burning fossil fuels and deforestation. The concentration of carbon dioxide in the atmosphere has been steadily increasing due to these human activities, leading to an enhanced greenhouse effect and global warming.

Opaque to Outgoing Terrestrial Radiation:
Carbon dioxide molecules have the ability to absorb and re-emit infrared radiation in the wavelength range of the Earth's outgoing terrestrial radiation. This means that when the Earth's surface emits heat energy as infrared radiation, carbon dioxide molecules in the atmosphere can absorb and trap some of this radiation, preventing it from escaping into space. As a result, the presence of carbon dioxide in the atmosphere contributes to the warming of the Earth's surface and the overall greenhouse effect.

Conclusion:
In summary, carbon dioxide is opaque to the outgoing terrestrial radiation because it absorbs and traps the heat energy emitted by the Earth's surface. This phenomenon, known as the greenhouse effect, is essential for regulating the Earth's temperature and maintaining a habitable environment. The increasing concentration of carbon dioxide in the atmosphere due to human activities is a major concern as it contributes to global warming and climate change.