ANS:A - remove hydrogen.

Phosphorus is indeed added to copper melt to remove hydrogen. When copper is melted or processed, it can absorb hydrogen from various sources such as moisture in the air or from the fuel used for heating. The presence of hydrogen in copper can lead to several issues including embrittlement, reduced ductility, and formation of internal defects like porosity. These hydrogen-related problems can significantly compromise the mechanical properties and quality of the copper. Phosphorus has a high affinity for hydrogen. When phosphorus is added to the molten copper, it reacts with the dissolved hydrogen to form phosphides, which then rise to the surface and can be removed as slag or dross. This process effectively removes hydrogen from the copper, helping to mitigate the associated problems such as embrittlement and porosity. Therefore, one of the important reasons for adding phosphorus to copper melt is indeed to remove hydrogen, thus improving the overall quality and properties of the copper.