The correct answer is: A. Gold
Gold is a chemical element with the symbol Au and atomic number 79. It is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, such as calaverite, chrysocolle, and chrysocolla, and in trace amounts in the mineral pyrite.
Gold is resistant to most acids, but will dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid. Gold is also soluble in a solution of sodium cyanide in the presence of oxygen.
Gold has been used for jewelry and other decorative purposes since prehistoric times. It is also used in coinage, dentistry, and electronics.
Silver is a chemical element with the symbol Ag and atomic number 47. It is a soft, white, lustrous transition metal. It is an excellent conductor of electricity and heat. Silver is also used in jewelry, photography, and silverware.
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal and is a member of the alkali metals group in the periodic table. It is the sixth most abundant element in the Earth’s crust and the seventh most abundant element in the universe by mass. Sodium is a major component of seawater and is found in many minerals. It is also used in many industrial processes, including the production of glass, soap, and detergents.
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile, malleable, and highly conductive metal with a reddish-brown color. Copper is one of the most widely used metals in the world, and is a major component of many alloys, including brass and bronze. Copper is also used in electrical wiring, plumbing, and roofing.