The correct answer is: B. Gold
Gold is a chemical element with the symbol Au and atomic number 79. It is a dense, soft, malleable, and ductile metal with a bright yellow color. 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.
Gold is resistant to most acids, but it is soluble 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 as a currency and a store of value for thousands of years. It is also used in jewelry, dentistry, and electronics.
The valleys of Son and Subarnarekha are located in the Indian states of Jharkhand and Odisha. These valleys are rich in gold deposits. The gold in these valleys is found in the form of nuggets, grains, and veins. The gold is mined by open-pit and underground mining methods.
The gold from the valleys of Son and Subarnarekha is of high quality. It is used in jewelry, dentistry, and electronics. The gold from these valleys is also exported to other countries.