Two liquids $X$ and $Y$ form an ideal solution. At $300 \ K,$ vapour pressure of the solution containing $1 \ mol$ of $X$ and $3 \ mol$ of $Y$ is $550 \ mm \ Hg.$ At the same temperature,if $1 \ mol$ of $Y$ is further added to this solution,vapour pressure of the solution increases by $10 \ mm \ Hg.$ Vapour pressure (in $mm \ Hg$) of $X$ and $Y$ in their pure states will be,respectively:

• A
  $300$ and $400$
• B
  $400$ and $600$
• C
  $500$ and $600$
• D
  $200$ and $300$