Two identical spheres each of radius `R` are placed with their centres at a distance `nR`, where `n` is integer greater than `2`. The gravitational force between them will be proportional to

Two metal spheres each of radius r are kept in contact with each other. If d is the density of the material of the sphere,then the gravitational force between those spheres is proportional to

Two identical solid copper sphere of radius R are placed in contact with each other. The gravitational force between them is proportional to.

Two spheres, each of mass 625 kg, are placed with their centres 50 cm apart. The gravitational force between them is