The correct answer is: B. 24% of nickel
Invar is an alloy of iron and nickel with a very low coefficient of thermal expansion. It is used in applications where dimensional stability is important, such as in watches, meters, and other precision instruments.
The composition of invar varies, but it typically contains 24% nickel. The nickel atoms in invar are arranged in a way that prevents them from moving easily when the material is heated or cooled. This makes invar very resistant to changes in size and shape.
Invar is also very strong and ductile, making it ideal for a variety of applications. It is a non-magnetic material, which makes it useful in applications where magnetism is a concern.
Invar is a valuable material for a variety of applications. It is used in watches, meters, and other precision instruments. It is also used in machinery, construction, and other industries.
The other options are incorrect because they do not represent the correct percentage of nickel in invar.