0.2 % and 0.2 M are two different units as well two different concentrations. Citric acid being a solid phase compound at room temperature (25 degree Celsius) is measured as % (w/v). So add 0.2 gm of citric acid in 100 mL distilled water. Whereas, molarity depends upon molar mass of a compound. For this, 1 M of citric acid means 192.12 gm in 1000 mL distilled water. Hence, for 0.2 M it will be 38.42 gm of citric acid in 1000 mL or 3.84 gm of citric acid in 100 mL distilled water.