Q1: __________ is the hardest material out of the following.

ANS:A - Boron carbide

Boron carbide is a ceramic material composed of boron and carbon atoms. It has the chemical formula B4C. Boron carbide is renowned for its exceptional hardness, high melting point, low density, and excellent chemical resistance. Here are some key characteristics and applications of boron carbide:

1. Hardness: Boron carbide is one of the hardest known materials, ranking third after diamond and cubic boron nitride (CBN) in terms of hardness. Its hardness makes it suitable for various applications requiring wear resistance and abrasion resistance.
2. Abrasion Resistance: Due to its exceptional hardness, boron carbide is commonly used in abrasive applications, such as grinding wheels, abrasive powders, and cutting tools. It can effectively cut and grind hard materials such as metals, ceramics, and stone.
3. High Melting Point: Boron carbide has a very high melting point, exceeding 2700°C (4900°F). This high melting point makes it suitable for high-temperature applications, such as in refractory materials and thermal protection systems.
4. Low Density: Despite its high hardness and melting point, boron carbide has a relatively low density, making it lightweight compared to other hard materials like diamond. This property is advantageous in applications where weight reduction is desired, such as in lightweight armor systems.
5. Chemical Resistance: Boron carbide exhibits excellent chemical resistance to acids, alkalis, and most chemical reagents. This property makes it suitable for use in corrosive environments and chemical processing applications.
6. Armor Applications: Boron carbide is widely used in armor applications, including body armor, vehicle armor, and aircraft armor. Its combination of high hardness, low density, and excellent ballistic resistance makes it an ideal material for protecting against ballistic threats.