The correct answer is C. Alnico.
Alnico is a strong permanent magnet made from an alloy of aluminium, nickel, cobalt, and iron. It is one of the most common types of permanent magnets, and is used in a variety of applications, including motors, generators, loudspeakers, and sensors.
Duralumin is an alloy of aluminium, copper, magnesium, and silicon. It is a strong, lightweight alloy that is used in a variety of applications, including aircraft, automobiles, and machinery.
Stainless steel is a type of steel that is resistant to corrosion. It is made from a variety of alloys, including iron, chromium, nickel, and molybdenum. Stainless steel is used in a variety of applications, including kitchen appliances, cutlery, and building materials.
Magnalium is an alloy of aluminium and magnesium. It is a lightweight, strong alloy that is used in a variety of applications, including aircraft, automobiles, and machinery.
Alnico is the only alloy listed that is used in making magnets.