Some scientists study asteroids that could potentially impact Earth Which mechanism could be used to best protect against this type of possible natural hazard?

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.

i think that the answer is c