The correct answer is: A. Lithium
Lithium is a soft, silvery-white metal that is the lightest of all metals. It is highly reactive and is the only metal that is liquid at room temperature. Lithium is used in batteries, alloys, and lubricants.
Sodium is a soft, silvery-white metal that is highly reactive. It is the sixth most abundant element in the Earth’s crust and is found in salt water. Sodium is used in many industrial processes, including the production of glass, soap, and paper.
Francium is a highly radioactive element that is the most reactive of all the alkali metals. It is so radioactive that it does not exist in nature and must be created in a laboratory. Francium is used in research on nuclear reactions.
Cerium is a silvery-white metal that is found in many minerals. It is used in alloys, ceramics, and glass. Cerium is also used in the production of hydrogen fuel cells.
Lithium is the only metal that is liquid at room temperature. This is because it has a very low melting point of 180 degrees Celsius. The other metals in the question have melting points that are much higher than room temperature.