A sample of water is contamniated with 30 ppm of arsenic (As). The molality of As in water is (Aw of As = 75.0 g)

30 g As is present in 106 g of water∴ Percentage of mass of As = 30×100106 = 3.0 ×10-3m = W2×1000Aw2×W1= 30×100075×106=0.4×10-3=4.0×10-2