A sample of water is found to contain 5.85% \((\frac{w}{w})\) of AB (molecular mass 58.5) and 9.50% \((\frac{w}{w})\) XY2 (molecular mass 95). Assuming 80% ionisation of AB and 60% ionisation of XY2 , the freezing point of water sample is
[Given : Kf for water 1.86 K kg mol-1 , Freezing point of pure water is 273 K and A, B and Y are monovalent ions]