Which is considered the “world’s most harmful fuel to the atmosphere? ”
oil shale
natural gas
coal
tar sands

The correct option is COAL.
Fuels are considered to be harmful to the atmosphere because of the carbon dioxide and other gases which are released into the atmosphere when these fuels are burned. Out of all these gas pollutants, carbon dioxide is the major pollutant of the atmosphere. Coal is considered to be the most harmful to the atmosphere because, its carbon dioxide content is much higher that that of the other fuels.