Question

give reason why it is dangerous to sleep in a closed room in which a coal fire is burning

Answer 1

It is not only dangerous but can also be fatal. Incomplete coal combustion produces carbon monoxide. When it is inhaled it reacts with haemoglobin to reduce its oxygen carrying capacity. Thus, it's a serious threat.
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Answer 2

it can be very dangerous for any human who is sleeping in a close room in which a coal Fire is burning because the coal is burning there, So the smoke will release there in maximum quantity that means carbon dioxide will release So the person sleeping in the room cannot take oxygen and can lead To death.