Which type of property cannot be seen just by observing with the senses

Explain why pure hydrogen cyanide does not conduct electricity, but become a conductor when it is dissolved in water? (at room temp, pure hcn exists as a volatile liquid)

Which of the following observations indicates that there is a small, dense, positively charged part in the center of an atom? some uncharged particles are scattered by a gold foil. all uncharged particles are attracted towards a gold foil. all positively charged particles pass straight through a gold foil. some positively charged particles bounce back from a gold foil.

Define the kinetic molecular theory