Which of the following substances is useful for making permanent magnets?

Classify the following as amorphous or crystalline solids: Polyurethane,naphthalene,benzoic acid,teflon,potassium nitrate,cellophane,polyvinyl chloride,fibre glass,copper.

'Stability of a crystal is reflected in the magnitude of its melting points'. Comment. Collect melting points of solid water,ethyl alcohol,diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules?

Which one is an example of an amorphous solid?

State the uses of amorphous solids and describe the cleavage property of amorphous solids.

Which among the following solids is a non-polar solid?