A jar test was conducted with alum and it was found that optimum alum dosage obtained when 50 mL alum solution containing 1.0gm/L is added into 2 L of water. The concentration of alum dosage was:

Density of solution, $\rho=1 \mathrm{~g} / \mathrm{L} ; \mathrm{V}=50 \mathrm{~mL} \therefore \mathrm{W}=\mathrm{V} \rho=\left(50 \times 10^{-3}\right) \mathrm{g}=50 \mathrm{mg}$ Concentration $=\frac{50}{2} \mathrm{mg} / \mathrm{L}=25 \mathrm{mg} / \mathrm{L} \equiv 25 \mathrm{ppm}$