Answer:
The correct answer is option 'D'. Solder is the alloy that is commonly used for joining metals in electrical work. Solder is a fusible metal alloy that is used to create a permanent bond between two or more metal surfaces. It has a low melting point, typically ranging from 180 to 190 degrees Celsius, which allows it to be melted and used as a filler material in the joining process.

Properties of Solder:
Solder is primarily composed of tin and lead, although the lead content has been reduced in recent years due to health and environmental concerns. The most common type of solder used in electrical work is known as lead-free solder, which typically contains a combination of tin, copper, and silver.

Advantages of Solder:
Solder has several advantages that make it suitable for electrical work:

- Low Melting Point: The low melting point of solder allows it to be easily melted using a soldering iron or other heat source, making it convenient for joining metals.
- Good Electrical Conductivity: Solder has good electrical conductivity, which is essential for electrical connections. It ensures that the electrical current can flow smoothly through the joint without any significant resistance.
- Strong Bond: Solder forms a strong bond between the metal surfaces, creating a reliable and durable connection. This is important for ensuring the longevity and reliability of electrical circuits.
- Easy to Use: Solder is relatively easy to work with, making it suitable for both professionals and hobbyists. It can be applied to the joint using a soldering iron or a soldering gun, and it solidifies quickly to form a strong bond.

Applications of Solder:
Solder is widely used in various electrical applications, including:

- Circuit Board Assembly: Solder is used to join components on circuit boards, creating electrical connections between them.
- Wire and Cable Connections: Solder is used to join wires and cables, ensuring a secure and conductive connection.
- Electrical Repairs: Solder is often used to repair broken electrical connections or replace faulty components.
- Plumbing: Solder is also used in plumbing applications to join copper pipes and fittings, creating leak-free connections.

Overall, solder is a versatile and widely used alloy that is essential for joining metals in electrical work. Its low melting point, good electrical conductivity, and strong bonding properties make it the ideal choice for creating reliable electrical connections.

Solder is used because it melts at 200c.it flows into heated metals along the joints and distributes itself by capillary action and grips the two pieces together when it all cools.