3g of activated charcoal was added to 50mL of the acetic acid solution (0.06 N) in a flask. After an hour, it was filtered and the strength of the filtrate was found to be 0.042 N. The amount of acetic acid adsorbed (per gram of charcoal) is :

50mL of 0.06 N acetic acid solution contains 0.06 mol/L × 50mL/1000mL/L × 60g/mol = 0.180 g of acetic acid. After filtration, 50mL of 0.042 N acetic acid solution contains 0.042mol/L × 50 mL/1000 mL/L = 0.0126 g of acetic acid. Hence, the amount of acetic acid adsorbed on 3 g of activated charcoal is 0.180g − 0.126g = 0.054g. This is equal to 54 mg. Hence, the amount of acetic acid adsorbed on 1 g of activated charcoal is 54mg × 1g/3g = 18mg.