Which raw materials are primarily used in foundry moulding operations?

The correct choice highlights the primary materials utilized in foundry moulding operations, which are essential for creating molds that ensure the quality and integrity of casted products. Silica sand is a crucial component, as it possesses high melting points and a granular texture, making it an ideal medium for mold formation. Its properties allow for the creation of detailed molds while ensuring the mold can withstand the heat and pressure during the metal pouring process.

Bentonite, a type of clay, is added to increase the strength of the mold and improve its ability to withstand thermal shock. It helps the sand grains stick together, enhancing the integrity of the mold. The mention of flour or paste water indicates additional binding agents that can be mixed to achieve the desired consistency and workability, aiding in mold formation and performance. This combination of materials ensures optimal performance in the molding process, leading to better-quality castings with fewer defects.

Other choices do not adequately represent the standard materials used in foundry operations. For instance, while silica sand is present in several options, none match the combination and emphasis on bentonite, which plays a vital role in mold strength.