Which physical method can be used for obtaining a sample of salt from a small beaker of salt water?
boiling
freezing
chromatography
sorting

Boiling.

Explanation:

Solution is a uniform composition and can be separated by physical methods.Boiling is the process of fast evaporation of water, that a liquid is boiled to its boiling point.Boiling point is the temperature at which the condensation pressure of the liquid is equal to the force used on the liquid by the nearby environment.Boil the water till complete water evaporation, water evaporates and salt remain in the beaker.  

So, the right choice is: Boiling.

Copper, silver, aluminum, cobalt, chromium, mercury 

Well to my expert knowledge and my exquisite calculations i think the the negative ion # 412 is the key to sucess