Q1: __________ can replace tungsten in high speed steel.

ANS:C - Cobalt

Cobalt is a metallic element with the chemical symbol Co and atomic number 27. It is a hard, brittle, silver-gray metal that is ferromagnetic at room temperature. Cobalt has a number of important applications across various industries:

1. Alloying Element: Cobalt is widely used as an alloying element in the production of various alloys. For example, cobalt is commonly used in the production of high-speed steels (HSS), where it enhances the hardness and red hardness of the steel, contributing to its ability to retain hardness at elevated temperatures. Cobalt-based superalloys are also utilized in the aerospace industry for their high-temperature strength and corrosion resistance.
2. Catalysis: Cobalt compounds are used as catalysts in chemical reactions. Cobalt catalysts are employed in processes such as petroleum refining, hydrogenation reactions, and the production of synthetic fuels.
3. Battery Materials: Cobalt is a key component in the cathodes of lithium-ion batteries, which are used in various applications such as electric vehicles, portable electronics, and energy storage systems. Cobalt-based cathodes offer high energy density and stability, making them essential for advanced battery technologies.
4. Medical Applications: Cobalt-based alloys are used in medical implants and prosthetic devices due to their biocompatibility, corrosion resistance, and mechanical properties. Cobalt-chromium alloys, for example, are commonly used in orthopedic implants such as hip and knee replacements.
5. Pigments: Cobalt compounds are used as pigments in ceramics, glass, and paints. Cobalt blue pigment, made from cobalt(II) aluminate, is known for its vibrant blue color and has been used in artistic and industrial applications for centuries.
6. Radioactive Isotopes: Certain isotopes of cobalt, such as cobalt-60, are radioactive and have applications in medical imaging (gamma ray sources for cancer therapy and sterilization) and industrial radiography (non-destructive testing).