$11.$ Compare the efficiency and environmental impact of coal gasification versus coal liquefaction. Which process do you consider more sustainable in the long term?

$12.$ Detail the steps involved in the high temperature carbonization of coal. What are the main products and by$-$products of this process?

$13.$ What are the main challenges associated with the liquefaction of solid fuels? Discuss the technological and environmental hurdles that need to be overcome.

$14.$ Describe the process of low temperature carbonization of coal. What are its applications, and how does it differ from high temperature carbonization?