Answer:
1,2: When simple molecular substances melt or boil, it is these weak intermolecular forces that are overcome. The covalent bonds are not broken. Relative little energy is needed to overcome the intermolecular forces, so simple molecular substances have a low melting and boiling points.
3: Water, Almost no living thing can survive without water. Water is everywhere on our planet. It is the reason we have an organic life on earth. A water molecule consists of one oxygen atom combined with two hydrogen atoms. We use water throughout day and night; in drinking, cooking, household needs, industries, and agriculture. Apart from these general uses of water, you might be amazed to know that water plays a major role in volcanic eruptions.