why or how does non-volatile impurity forms strong bond with water
If an impurity is present in a pure substance, the boiling point of the substance will be increased. Take the example of water. Pure water should boil at 100? Celsius. However, if you add granules of salt to water before boiling it, the presence of the salt may result in raising the boiling point of this solution by as much as one or two degrees Celsius.
The reason why the boiling point of the substance is raised is because the two components in the solution - in this case, the water and the salt - form chemical bonds with each other. These bonds require a lot of energy in order to break them. In this case, the bonds are being broken by heat energy, when the solution is heated to temperatures of over 100? Celsius. However, it requires more heat energy to break the bonds in order to boil the water, than it takes to simply boil pure water on its own. As more heat energy is required, the boiling point of the solution increases.
It may help you to think of the impurity - in this case, the salt - as a magnet or glue, holding the solution in its liquid form. In order for the liquid to change into its gaseous form when it reaches its boiling point, the liquid needs to break contact with the magnet or the glue, and this requires more heat energy.