GEOLOGY

Detailed explanation-1: -(b) Magnetite, Bar magnet, Dumbbell-shaped magnet, Horseshoe magnet Magnetite is an iron ore which is a natural magnet while the others are artificial magnets.

Detailed explanation-2: -Iron, Nickel, and Cobalt are the magnetic substances as objects made up of these materials are attracted by a magnet.

Detailed explanation-3: -Examples of magnetic substances include iron, nickel, cobalt, stainless steel, and many rare earth metals. Diamagnetic materials like copper and gold are weakly repelled by a magnetic field. Paramagnetic materials like calcium and aluminum are weakly attracted by a magnetic field.

Detailed explanation-4: -Gadolinium, samarium and neodymium are all examples of magnetic rare earth metals. Various magnets with different properties can be manufactured using the above metals in combination with iron, nickel and cobalt. These magnets come with specific properties necessary for certain applications.