Ionic compounds are very strong in nature. They require a lot of energy to break them. Therefore they have high melting and boiling points.

Ionic compounds can conduct electricity only if their ions are free to move. Hence they behave as conductors when they are dissolved in water.

Graphite is made up of carbon layer that can slide over each other. Like metals, the electrons are free to move. Whereas, the rest of the compounds are made up of carbon atoms held together tightly. Therefore, graphite is the covalent compound that conducts electricity.

Crystalline solids are those in which atoms are arranged in an orderly fashion. They have directional properties and therefore are called anisotropic substances.

Glasses of the building appear milky because it undergoes heating during the day and cooling during the night. Therefore it acquires some crystalline properties.