A. Underground coal mining is dangerous because of possible tunnel collapse and possible methane gas explosions.
Explanation:
Dangers of underground coal mining include asphyxiation, methane gas poisoning, tunnel collapse and explosions of methane gas, a highly flammable gas. Methane explosions occur since this gas is a byproduct of coal. This explosion can cause tunnel collapse.
Atoms can gain or lose electrons and become ions, which are atoms that have a positive or negative charge, because they have unequal numbers of protons and electrons.
A primary source is a first hand account of an event while a secondary source is a retelling or second hand account meaning as many details will be prevalent.
