Chemical Engineering - Heat Transfer - Discussion

Gases also absorbed heat. Should they not be considered opaque?

Most solids are opaque to thermal radiation except glass, rock salt etc.

Many liquids and gases are transparent to thermal radiation.

A body is considered transparent if it can transmit some of the radiation waves falling on its surface. If electromagnetic waves are not transmitted through the substance it is therefore called opaque. When radiation waves hit the surface of an opaque body, some of the waves are reflected back while the other waves are absorbed by a thin layer of the material close to the surface. For engineering purposes all materials are thick enough that they can be considered opaque.

Then how does the sunlight reach to the aquatic plants.