Amagnet is passed ten centimeters above a desk. A paper clip resting on the desk begins to move as the magnet passes over it. What could be done to increase the effect of the magnet on the paper clip?​

use a stronger magnet:

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

the answer is c.the valence of the atoms combine .