Coal releases carbon dioxide when burned. The reaction looks like this:
C(s)+O₂(g)→CO₂(g)
I hope this helps. Let me know in the comments if anything is unclear.
Answer: Because new substances are formed.
Explanation: A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity. Once a chemical change occurs it cannot be undone due to the change in chemical identity. The creation of a new substance is not reversible.
Answer: a) 
b) 1 mole of
is produced.
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.
The skeletal equation is:

The balanced equation will be:

Thus the coefficients are 2, 3 , 10 , 4 , 3 , 2 and 5.
b) Oxidation: 
Reduction: 
Net reaction: 
When 1 mole of
is produced, 1 mole of
is produced.