Liquids $A$ and $B$ form an ideal solution over the entire range of composition. At temperature $T$,an equimolar binary solution of liquids $A$ and $B$ has a vapour pressure of $45 \ Torr$. At the same temperature,a new solution of $A$ and $B$ having mole fractions $x_A$ and $x_B$,respectively,has a vapour pressure of $22.5 \ Torr$. The value of $x_A / x_B$ in the new solution is . . . . . (Given that the vapour pressure of pure liquid $A$ is $20 \ Torr$ at temperature $T$)

• A
  $10$
• B
  $12$
• C
  $15$
• D
  $19$