The correct answer is: b) Medium-grade.
Coal is a fossil fuel formed from the remains of ancient plants and animals that have been buried and subjected to intense heat and pressure over millions of years. It is a non-renewable resource that is used to generate electricity, produce steel, and make other products.
The quality of coal is determined by its carbon content, ash content, sulfur content, and heating value. High-grade coal has a high carbon content, low ash content, low sulfur content, and high heating value. Medium-grade coal has a lower carbon content, higher ash content, higher sulfur content, and lower heating value than high-grade coal. Low-grade coal has the lowest carbon content, highest ash content, highest sulfur content, and lowest heating value of all types of coal.
The quality of coal found in Arunachal Pradesh is generally medium-grade. It has a carbon content of about 70%, an ash content of about 10%, a sulfur content of about 0.5%, and a heating value of about 6,000 BTU per pound.
The quality of coal found in Arunachal Pradesh is not as high as the quality of coal found in some other parts of the world, such as Australia and South Africa. However, it is still a valuable resource that can be used to generate electricity, produce steel, and make other products.