ANS:C - castability

The addition of silicon to aluminum improves its castability. Aluminum-silicon alloys are commonly used in casting applications due to their improved fluidity, shrinkage resistance, and ability to fill intricate molds effectively. The addition of silicon to aluminum alters its microstructure and solidification behavior, resulting in alloys that exhibit better casting characteristics. Silicon helps reduce the tendency of aluminum to shrink and crack during solidification, which enhances the overall castability of the alloy. While aluminum-silicon alloys may exhibit some variations in corrosion resistance and machinability depending on the specific composition and processing conditions, the primary benefit of silicon addition in aluminum alloys is improved castability. Therefore, the correct answer is: Addition of silicon to aluminum improves its castability.