A non-volatile solute, ‘A’, tetramerizes in water to the extent of 80%. 2.5 g of ‘A’ in 100 g of water lowers the freezing point by 0.3°C. The molar mass of A in $ \text{g/mol} $ is (with $ K_f $ for water = 1.86 $ \text{K kg mol}^{-1} $).