A compound differs from an element in that it can be decomposed by a chemical reaction.
A compound, by definition, is made up of two or more elements that have been combined together through a chemicalbond.
Thus, the chemical bond or bonds in a compound can be decomposed by a chemical reaction giving rise to the individual elements that make up the compound.
This is unlike an element that can not be decomposed by any chemical reaction.
The correct answer is a.) C. Oxidation occurs when an element loses electrons and increases its oxidation state. In the chemical equation, Carbon in CH4 has an oxidation state of 4- while Carbon in CO2 has an oxidation of 4+.