1. The effect of the impurity on the mixture caused the melting point of the mixture to be lowered.
2. The reason why the melting point of a binary mixture is lowered, is due to the fact that the mixture of the two components has caused the structure of the solid to change and become less organized (not as strong). Therefore causing the mixture to melt at a lower temperature. The melting point is broadened because the mixture has more than one component present; which means it will take a longer period of time to melt, because there will be more than one solid structure to break down, therefore broadening the melting point of the mixture. Compared to the melting point of either component of the mixture, the melting point of the mixture will be lower. The melting points of the components will be higher because they are pure substances. The fact that they are pure substances means that the solid has an organized structure (strong); the bonds will therefore be harder to break causing the melting point of the components to be higher and sharper.
3. Salt or urea dissolves in water as ions of chlorine and sodium .The ions either hydrate or join as a part of the water molecules, producing heat on icy surfaces to thaw the ice.
It can be concluded that the melting point of the substances: naphthalene (81°C-85°C), biphenyl (71°C-73°C), and a mixture of C (42°C-56°C) can be determined by placing a small amount of the substance in a capillary tube attached to a thermometer, in heating water and then taking the temperature of the substance (when it first begins to melt and as soon as it has completely melted).