At 300 K vapour pressure of a pure liquid, 'A' is 70 mm Hg. It forms an ideal solution with another liquid ' B '. The mole fraction of B in the solution is 0.2 and total vapour pressure of solution is 84 mm Hg at same temperature. What is the vapour pressure $(\mathrm{in} \mathrm{mm})$ of pure liquid B at 300 K ?

• Correct answer
  A

  140
• B

  70
• C

  280
• D

  560

Hence, the correct answer is option: 'A'.