C8H18 is a hydrocarbon, which means it consists of hydrogen and carbon atoms only. (i) Cracking: It is a process of breaking down larger hydrocarbons into smaller hydrocarbons. C8H18 can undergo cracking, which means it can break down into smaller hydrocarbons. (ii) Combustion: It is a reaction between a substance and oxygen in the presence of a flame or spark. C8H18 can undergo combustion and produce carbon dioxide and water. (iii) Substitution: It is a reaction in which an atom or group of atoms is replaced by another atom or group of atoms. C8H18 can undergo substitution if it reacts with a suitable reagent. (iv) Addition: It is a reaction in which two or more reactants combine to form a larger product. C8H18 can undergo addition if it reacts with a suitable reagent. Therefore, C8H18 can undergo all of the above reactions. So, the answer is None.