It is harmful because you can get burned easy and your clothes can get dirty.
Decrease the temperature of the oxygen because if coal goes air born it can explode and wipe out power plants like they were not there
Molecular weight calculation:
24.305 + (15.9994 + 1.00794)*2
Molar mass of Mg(OH)2 = 58.31968 g/mol
The answer is N. Hope this helped