Explanation:
The given data is as follows.
     [tex]t_{m}[/tex] = 30.0 sec,   [tex]t_{r1}[/tex] = 5 min = [tex]5 \times 60 sec[/tex] = 300 sec
     [tex]t_{r2}[/tex] = 12.0 min = [tex]12 \times 60 sec[/tex] = 720 sec
Formula for adjusted retention time is as follows.
   [tex]t'_{r} = t_{r} - t_{m}[/tex]
         = 300 sec - 30.0 sec
         = 270 sec
  [tex]t'_{r2}[/tex] = 720 sec - 30 sec
              = 690 sec
Formula for relative retention ([tex]\alpha[/tex]) is as follows.
     [tex]\alpha = \frac{t'_{r2}}{t'_{r1}}[/tex]
           = [tex]\frac{690 sec}{270 sec}[/tex]
           = 2.56
Thus, we can conclude that the relative retention is 2.56.
