A mixture of toluene and benzene forms a nearly ideal solution. Assume ${\mathrm{P}}_{\mathrm{B}}°$ and ${\mathrm{P}}_{\mathrm{T}}°$ to be the vapor pressures of pure benzene and toluene, respectively. The slope of the line obtained by plotting the total vapor pressure to the mole fraction of benzene is:-

• Correct answer
  A

  ${\mathrm{P}}_{\mathrm{B}}°-{\mathrm{P}}_{\mathrm{T}}°$
• B

  ${\mathrm{P}}_{\mathrm{T}}°-{\mathrm{P}}_{\mathrm{B}}°$
• C

  ${\mathrm{P}}_{\mathrm{B}}°+{\mathrm{P}}_{\mathrm{T}}°$
• D

  $\left({\mathrm{P}}_{\mathrm{B}}°+{\mathrm{P}}_{\mathrm{T}}°\right)/2$

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