How many parts per million of mercury are there in a sample of tap water with a. mass of 750 g containing 2.2 mg of hg

Parts Per Million is defined as the number of parts of a solute per one million parts of a solution.

                   ppm  =  (Weight of Solute / Weight of Solution) × 10⁶

Data Given;
                  Weight of Solute (Hg)  =  2.2 mg  =  0.0022 g

                  Weight of Solution (Tap Water)  =  750 g

Putting Values,
 
                  ppm  =  (0.0022 g / 750 g) × 10⁶

                  ppm  =  2.93 × 10⁻⁶ × 10⁶

                  ppm  =  2.93 

Result:
           It means if given tap water is containing 1 million particles then 2.93 particles in that are of Hg.

The correct answer is "atomic weight".