$19.$ Explain how briquetting can enhance the utility of low$-$grade coal. Discuss the process and the properties of the resulting briquettes.

$20.$ Detail the environmental benefits and drawbacks of converting coal into gas or liquid fuels. How do these processes affect carbon emissions and air quality?

$21.$ Discuss the importance of moisture content in the storage of coal. How does it affect the spontaneous combustion of coal and the overall energy content?

$22.$ Explain the technological advancements in coal liquefaction that have made it more viable as an alternative fuel source.