The correct answer is (a) Lithium.
Lithium is the lightest metal and the lightest solid element. It is a silvery-white metal that is soft and easily cut with a knife. It is also very reactive and must be stored in an inert atmosphere.
Beryllium is a light, strong, and brittle metal. It is the second lightest metal after lithium. Beryllium is used in a variety of applications, including aerospace, nuclear energy, and electronics.
Zinc is a blue-white metal that is used in a variety of applications, including galvanizing steel, batteries, and alloys. Zinc is the fourth most abundant metal in the Earth’s crust.
Sodium is a soft, silvery-white metal that is highly reactive. It is the sixth most abundant element in the Earth’s crust. Sodium is used in a variety of applications, including batteries, soaps, and glass.