The ratio of volumes of two spheres, whose radii are in the ratio 1 : 2, is :

The correct answer is (b) 1 : 8.

The volume of a sphere is given by the formula $V = \frac{4}{3}\pi r^3$, where $r$ is the radius of the sphere.

If the radii of two spheres are in the ratio 1 : 2, then the volumes of the spheres are in the ratio $1^3 : 2^3 = 1 : 8$.

Option (a) is incorrect because the volumes of the spheres are not in the ratio 1 : 2.

Option (c) is incorrect because the volumes of the spheres are not in the ratio 1 : 4.

Option (d) is incorrect because the volumes of the spheres are not in the ratio 2 : 7.