Two planets of radii r1 and r2 are made from the same material. The ratio of the acceleration due to gravity g1/g2 at the surface of the two planets is
$\dfrac{r_{1}}{r_{2}}$
$\dfrac{r_{2}}{r_{1}}$
$\left(\dfrac{r_{1}}{r_{2}}\right)^{2}$
$\left(\dfrac{r_{2}}{r_{1}}\right)^{2}$