Why is it dangerous to burn coal in a closed room?

Monika read in a newspaper that a man became unconscious because of burning coal in a closed room. The teacher told her that during burning coal, a gas is produced which causes death of a person. Name this gas

Why is it dangerous to stand on the edge of the platform near the railway line when the train is passing by?

What is the latest use of coal- gas?

Name the most dangerous opiate?

A diamond glitters in a brightly lit room, but not in a dark room. Why?