Two examples of natural substances are:

1. Water: Water is one of the most abundant and essential natural substances on Earth. It is found in oceans, rivers, lakes, and underground reservoirs, and it plays a crucial role in supporting life and various natural processes.

2. Wood: Wood is a natural material derived from the stems and branches of trees. It is used for construction, fuel, furniture, paper, and numerous other applications. Wood is renewable and biodegradable, making it an environmentally friendly material choice.

The purest form of carbon is typically considered to be diamond. Diamond consists of carbon atoms arranged in a crystal lattice structure, with each carbon atom bonded to four other carbon atoms in a tetrahedral arrangement. This structure is exceptionally stable and gives diamond its remarkable hardness, optical properties, and thermal conductivity.

Diamond is composed entirely of carbon atoms and is formed under high pressure and temperature conditions deep within the Earth's mantle. It is prized for its brilliance, clarity, and durability, making it a highly valuable gemstone for use in jewelry and industrial applications, such as cutting, grinding, and drilling.

Other forms of carbon, such as graphite and graphene, also consist of pure carbon atoms but have different atomic arrangements and properties. Graphite, for example, consists of carbon atoms arranged in layers that can slide over each other, giving it lubricating properties. Graphene is a single layer of carbon atoms arranged in a hexagonal lattice and exhibits exceptional strength, conductivity, and flexibility.

The main use of coke is as a fuel and reducing agent in the production of iron and steel through the process of smelting in a blast furnace. Coke is a porous, hard, and grayish-black solid substance obtained by heating coal in the absence of air to drive off volatile compounds. This process, known as coking or carbonization, produces coke with a high carbon content (typically over 90%).

In the steelmaking process, coke serves several important functions:

1. Fuel: Coke is burned in the blast furnace to provide the high temperatures needed for smelting iron ore into molten iron. It serves as a source of heat energy, allowing the iron ore to be reduced to iron metal through chemical reactions.

2. Reducing Agent: Coke acts as a reducing agent, facilitating the conversion of iron ore (mainly iron oxide, Fe2O3 or Fe3O4) into metallic iron (Fe). In the blast furnace, carbon monoxide (CO) gas is produced by the combustion of coke with oxygen (O2) from the air. The carbon monoxide then reacts with the iron ore, reducing it to iron according to the following reaction: Fe2O3(s)+3CO(g)→2Fe(s)+3CO2(g)Fe2O3(s)+3CO(g)→2Fe(s)+3CO2(g) This reaction allows the iron to be separated from impurities and formed into molten pig iron.

3. Heat Generation: In addition to serving as a source of heat energy, the combustion of coke also generates carbon dioxide (CO2) gas, which helps to agitate and mix the contents of the blast furnace, ensuring efficient chemical reactions and heat distribution.

4. Chemical Stability: Coke has a high carbon content and is chemically stable at high temperatures, allowing it to maintain its structural integrity and provide consistent fuel and reducing properties throughout the smelting process.

Overall, coke is indispensable in the production of iron and steel, playing a crucial role in providing heat, reducing iron ore, and ensuring the efficient operation of blast furnaces in the steelmaking industry.

Two fractions of petroleum are:

1. Gasoline (Petrol): Gasoline, also known as petrol in some regions, is a volatile liquid fraction of petroleum. It is primarily used as fuel for internal combustion engines in vehicles such as cars, motorcycles, and light trucks. Gasoline is a mixture of hydrocarbons with varying chain lengths, typically consisting of molecules containing between 4 and 12 carbon atoms. It is obtained through the fractional distillation of crude oil and is further processed in refineries to meet specific performance and environmental requirements.

2. Diesel: Diesel is another liquid fraction of petroleum, typically obtained through the fractional distillation of crude oil. It consists of hydrocarbon molecules with longer chain lengths compared to gasoline, typically containing between 10 and 20 carbon atoms per molecule. Diesel fuel is commonly used as fuel for diesel engines, which are widely used in heavy-duty vehicles such as trucks, buses, locomotives, and ships, as well as in industrial machinery and generators. Diesel fuel is valued for its high energy density, efficiency, and relatively low emissions compared to gasoline.