The solubility of potassium nitrate in water at 75°C is 155 g/100 g and at 20°C is 31 g/100 g. What mass of potassium nitrate must be taken to give 100 g of crystals when a
saturated solution at 75°C is cooled to 20°C?

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

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