The correct answer is (b), coal. Lignite is a type of coal that is less mature than bituminous coal and anthracite coal. It is also known as brown coal or soft coal. Lignite is formed from plant material that has been buried and subjected to heat and pressure over millions of years. It is a relatively soft, low-grade coal that has a high moisture content. Lignite is used primarily to generate electricity.
Limestone is a sedimentary rock that is composed primarily of calcium carbonate. It is formed from the remains of marine organisms, such as coral and algae. Limestone is used in a variety of construction applications, including as a building material, as a road base, and in the manufacture of cement.
Iron ore is a mineral that is used to produce iron. It is found in rocks and minerals that are rich in iron. Iron ore is mined and then processed to extract the iron. Iron is used to make a variety of products, including steel, iron castings, and wrought iron.
Copper is a metal that is found in nature. It is a reddish-brown color and is a good conductor of electricity. Copper is used in a variety of applications, including electrical wiring, plumbing, and roofing.