A fine grained grinding wheel should not be used for grinding __________ materials.

ANS:C - soft & ductile

A fine-grained grinding wheel should not be used for grinding soft and ductile materials. Grinding wheels with fine grains are typically used for precision grinding tasks where a smooth finish and tight tolerances are required. These wheels are effective for grinding hard and brittle materials because they can remove material at a controlled rate without causing excessive damage to the workpiece. However, when used on soft and ductile materials, fine-grained grinding wheels may tend to clog with material, resulting in poor grinding performance, increased heat generation, and potential damage to the workpiece surface. Soft and ductile materials may deform and smear rather than being efficiently removed by the grinding action of fine-grained wheels. In contrast, coarse-grained grinding wheels are better suited for grinding soft and ductile materials as they provide more aggressive cutting action and are less prone to clogging. Therefore, it is generally recommended to use coarse-grained wheels for grinding soft and ductile materials to achieve optimal results.