Answer: (3) ppm
Explanation: Concentration is defined as the amount of solute dissolved in a known amount of the solvent or a solution.
Parts per million (ppm) is used to express the concentration when a very small quantity of solute is present in a large quantity of the solution. It is defined as the mass of solute present in one milion
parts by mass of the solution.

L/s is used to express flow rate.
J/g is used to express energy per unit mass.
kPa is used to express pressure.
Hydrogen is different from alkali metals because it also exhibits the properties of inert gas
When you add a pinch of baking soda into vinegar, carbon dioxide gas is produced