The substance which is called black gold is available in earth’s crust but is not abundant. It is referred to gold due to its high worth. It is a common fossil fuel. Complete step by step answer: -As we can understand from the name itself, the substance which is called black gold is black in colour. -As we know, gold is a noble, scarcely available and an expensive metal similarly, black gold is also referred to as gold due to its price and value. -The term Black Gold is used to refer to oil or petroleum. -Petroleum is a naturally occurring yellowish-black liquid found beneath the Earth’s surface. -It is generally refined and various fuels are formed from it. -It consists of naturally occurring hydrocarbons of different molecular weights but it also contains some other organic compounds. Each petroleum variety has a unique mixture of molecules which defines its physical property like colours, density and viscosity. -The name petroleum is referred to both naturally occurring crude oil and also the petroleum products which are formed from the crude oil. -Petroleum is called ‘Black Gold’ due to the following reasons- -When petroleum is extracted from the ground, the crude oil is black in colour. -It is compared to gold due to its high commercial value and due to its valuable properties. -It is rare on earth and not easily found. -Its extraction is also very expensive. -The extracted crude oil is black but after purification, it turns yellowish hence the name gold. Therefore, the correct answer is option C petroleum. Additional information The use of petroleum as a fuel increased global warming. It is a major cause for ocean acidification too. Note: It is important to remember here that it has no similar chemical or physical properties as gold. It is also not a metal like gold. It is called black gold simply due to its commercial value. Coal is also black and a common source of fuel but the term ‘black gold’ is not used for coal, it is used for petroleum.