The correct answer is $\boxed{\text{B}}$. Magnetite is a naturally occurring iron oxide mineral with the chemical formula Fe3O4. It is one of the most common minerals on Earth, and it is found in many different types of rocks. Magnetite is a black, opaque mineral that is strongly magnetic. It is used in a variety of applications, including magnets, magnetic recording media, and iron ore.
Option $\text{A}$, Fe2O3, is hematite. Hematite is a red, brown, or black mineral that is also an iron oxide. It is less magnetic than magnetite, but it is still used in some applications, such as pigments and abrasives.
Option $\text{C}$, FeCO3, is siderite. Siderite is
a white or gray mineral that is also an iron carbonate. It is not magnetic, and it is not used in the same applications as magnetite or hematite.Option $\text{D}$, 2Fe2O3. 3H2O, is goethite. Goethite is a yellow or brown mineral that is also an iron oxide. It is not magnetic, and it is not used in the same applications as magnetite, hematite, or siderite.