The dryness fraction of vapour after throttling process is

Question

Saturated liquid at a high pressure p₁ having enthalpy of saturated liquid 1000kJ/kg is throttled to a lower pressure p2 . At pressure p₂ enthalpy of saturated liquid and that of the saturated vapour are 800 and 2800 kJ/kg respectively. The dryness fraction of vapour after throttling process is                             

a. 0.1                           b. 0.5

c. 18/28                       d. 0.8