An aqueous solution has a mass of 490 grams containing 8.5 × 10-3 gram of calcium ions. the concentration of calcium ions in this solution is

1. 4.3 ppm
2. 8.5 ppm
3. 17 ppm
4. 34 ppm

To solve the concentration, it is equal to the mass of the calcium ions divided by the total mass of the solution.
C = mass of ions / mass solution
C = ( 8.5 x 10 ^-3 g ) / 490 g
C = 1.7 x 10^-5
since the choices are in ppm, multiply it by 10^6
C = (1.7 x 10^-5 ) 10^6
C = 17 ppm