What is the primary feature necessary for a monomer to make it useful in a condensation polymerization reaction?

What is the monomer of teflon? Give its important use?

What is meant by hysteresis loop? What type of magnetic material is used in making permanent magnets?

Explain why friction is necessary to make the disc in Fig. 7.41 roll in the direction indicated. (a) Give the direction of frictional force at B, and the sense of frictional torque, before perfect rolling begins. (b) What is the force of friction after perfect rolling begins?