Explanation:
Formula to calculate specific rotation is as follows.
    Specific rotation ([tex][\alpha][/tex]) = [tex]\frac{\alpha}{c} \times l[/tex]
where, Â Â [tex]\alpha[/tex] = observed rotation
          c = concentration in g/ml
          l = path length in dm
It is given that,
       [tex]\alpha = -6.16^{o}[/tex]  Â
        c = [tex]\frac{10 g}{500 ml}[/tex] = 0.02 g/ml
       l = 20 cm = 2 dm  (as 1 dm = 10 cm)
Therefore, calculate the specific rotation as follows.
   Specific rotation ([tex][\alpha][/tex]) = [tex]\frac{\alpha}{c} \times l[/tex]
            = [tex]\frac{-6.16^{o}}{0.02 g/ml} \times 2 dm[/tex]
            = [tex]-616^{o}[/tex]
Thus, we can conclude that the specific rotation of this compound is [tex]-616^{o}[/tex].