ANS:B - Tungsten carbide

The most wear-resistant grade of carbide used for cutting tools is Tungsten carbide. Explanation:

1. Aluminium carbide: While aluminium carbide is a compound that can be used in certain applications, it is not commonly used for cutting tools. It is not as wear-resistant as tungsten carbide.
2. Nickel carbide: Nickel carbide is also not commonly used for cutting tools. It does not possess the same level of wear resistance as tungsten carbide.
3. Iron carbide: Iron carbide, also known as cementite, is primarily a constituent of steel rather than a standalone cutting tool material. While it contributes to the hardness of certain steels, it is not as wear-resistant as tungsten carbide.
4. Tungsten carbide: Tungsten carbide is widely used in cutting tool applications due to its exceptional hardness, wear resistance, and toughness. It is composed of tungsten and carbon atoms in a one-to-one ratio, forming a hard and durable material that can withstand high-speed cutting operations and abrasive wear. Tungsten carbide cutting tools maintain their sharpness and cutting edge for extended periods, making them highly effective for machining a wide range of materials, including metals, composites, and ceramics.