Fill in the blanks : (a) A reaction in which two or more substances combine to form a single substance is called a ___ reaction. (b) A ___ is a substance which changes the rate of a chemical reaction without undergoing a chemical change. (c) The formation of gas bubbles in a liquid during a reaction is called___ (d) The reaction between an acid and a base is called ___ (e) Soluble bases are called ___ (f) The chemical change involving iron and hydrochloric acid illustrates a ___ reaction. (g) In the type of reaction called ___ two compounds exchange their positive and negative radicals respectively. (h) A catalyst either ___ or ___ the rate of a chemical change but itself remains ___ at the end of the reaction. (i) The chemical reaction between hydogen and chlorine is a ___ reaction (j) When a piece of copper is added to silver nitrate solutuions, it turns ___ in colour.