ANS:B - Invar is a magnetic alloy.

Invar is a type of alloy primarily composed of iron (Fe) and nickel (Ni), typically containing around 36% nickel and 64% iron. It is renowned for its unique thermal expansion properties, which make it highly valuable in precision engineering applications. Here's an explanation of why Invar is considered a magnetic alloy:

1. Composition: Invar is predominantly composed of iron and nickel, both of which are ferromagnetic elements. Iron is ferromagnetic at room temperature, while nickel becomes ferromagnetic at temperatures below its Curie point (about 358°C or 676°F). Therefore, the iron-nickel alloy in Invar retains some magnetic properties due to the presence of these ferromagnetic elements.
2. Magnetic behavior: While Invar does exhibit some magnetic properties due to the presence of iron and nickel, it is important to note that its magnetic behavior is relatively weak compared to materials like pure iron or nickel. Invar's magnetic susceptibility is much lower than that of pure iron or nickel, making it less responsive to external magnetic fields.
3. Magnetic applications: Despite its magnetic properties, Invar is often used in non-magnetic applications where its low coefficient of thermal expansion is the primary consideration. For example, Invar is commonly used in precision instruments, scientific equipment, and aerospace components where dimensional stability over a wide temperature range is crucial. In such applications, the weak magnetic properties of Invar are generally not a significant concern.

In summary, while Invar does contain ferromagnetic elements such as iron and nickel and exhibits some magnetic properties, its primary value lies in its unique thermal expansion characteristics rather than its magnetic behavior. Therefore, Invar is considered a magnetic alloy primarily due to the presence of iron and nickel, but its magnetic properties are typically of secondary importance in practical applications.