Which best describes a compound such as sodium chloride?
a pure substance that can be separated into different elements by physical means
a mixture of two common substances that can be separated by chemical means
a mixture of two common elements that can be separated by physical means
a pure substance that can be separated into different elements by chemical means

The second option is the answer.  This is a mixture of two common substances that can be separated by chemical means.

NaCL is a compound that was formed through a chemical  reaction between sodium and chlorine. In that reaction sodium  which is a toxic metal combines with chlorine, a poisonous gas, to form a harmless but totally new compound NaCl or table salt.

Since the sodium ions have a positive charge and the chlorine ions have a negative charge, they are attracted to each other to form an ionic bond. 

 Sodium can only be separated from Chloride by chemical means e.g.  electrolysis.

in chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. the standard formula is c = m/v, where c is the concentration, m is the mass of the solute dissolved, and v is the total volume