A light planet revolving around a very massive star in a circular orbit of radius R with a period of revolution T. If the gravitational force of attraction between the planet and star is proportional to $R^{\large\frac{-5}{2}}$ then $T^2$ is proportional to

Question

\[(a)\;R^3 \quad (b)\;R^{\frac{7}{2}} \quad (c)\;R^{\frac{3}{2}} \quad (d)\;R^{\frac{9}{2}}\]