There are three substances X, Y and Z. The substance X does not have a fixed melting point or boiling point and it still shows the individual properties of its constituents. The substance Y is a pure substance which occurs in nature as such. The substance Y has a fixed melting point and boiling point but it cannot be broken down into simpler substances by any chemical means. The substance Z is also a pure substance whose properties are entirely different from those of its constituents. The substance Z can, however, be divided by electrolysis into two substances which belong to the same class of substances as Y. (a) What type of substance could X be? Name one substance like X. (b) What type of substance could Y be? Name one substance like Y. (c) What type of substance could Z be? Name one substance like Z. (d) Which process involves absorption or release of an appreciable amount of energy: formation of substances X or formation of substance Z? (e) Name the three groups into which all the substances like Y are divided on the basis of their properties.