ANS:A - The emissivity of a surface decreases, if it gets corroded by atmospheric environment.

The statement "The emissivity of a surface decreases if it gets corroded by the atmospheric environment" is generally true. Emissivity is a measure of how efficiently a surface emits thermal radiation compared to an ideal blackbody at the same temperature. It is a dimensionless quantity ranging from 0 to 1, where a value of 1 indicates that the surface is a perfect emitter (blackbody), and lower values indicate lower emission efficiency. When a surface becomes corroded by exposure to the atmospheric environment, several changes can occur that affect its emissivity:

1. Surface Texture: Corrosion can lead to the formation of rough, irregular surface textures. These surface irregularities can scatter and reflect thermal radiation, reducing the effective radiating area of the surface and thus decreasing its emissivity.
2. Chemical Composition: Corrosion can alter the chemical composition of the surface, leading to the deposition of corrosion products or the formation of surface oxides. These surface layers may have different thermal properties than the original material, affecting their ability to emit thermal radiation efficiently.
3. Optical Properties: The presence of corrosion products or surface oxides may change the optical properties of the surface, such as its reflectivity and absorptivity. Depending on the specific composition and structure of the corrosion layer, these changes can either increase or decrease the surface emissivity.
4. Surface Contamination: Corrosion can also introduce surface contaminants or impurities that affect the thermal properties of the surface. These contaminants may alter the surface's ability to absorb and emit thermal radiation, leading to changes in emissivity.

Overall, while it's possible for corrosion to lead to a decrease in emissivity due to changes in surface texture, composition, and optical properties, the specific effect can vary depending on the nature of the corrosion and the material involved. Therefore, the relationship between corrosion and emissivity is complex and can depend on various factors.