The correct answer is: B. Uranium
Monazite sand is a heavy, black, or brown sand that is found in beach sands, river sands, and placer deposits. It is a complex phosphate mineral that contains the rare earth elements, thorium, and uranium. Monazite sand is used as a source of rare earth elements, thorium, and uranium.
Potassium is a soft, silvery-white metal that is found in nature as the mineral sylvite. Potassium is an essential element for plant and animal life. It is also used in fertilizers, batteries, and explosives.
Sodium is a soft, silvery-white metal that is found in nature as the mineral halite. Sodium is an essential element for plant and animal life. It is also used in table salt, soap, and glass.
Thorium is a radioactive metal that is found in nature as the mineral thorite. Thorium is used in nuclear reactors and as a source of light.
Uranium is a radioactive metal that is found in nature as the mineral pitchblende. Uranium is used in nuclear reactors and as a source of nuclear weapons.