It is the same, there is no difference.
In fact, the force of gravity on an object is equal to the weight of the object, defined as
[tex]W=mg[/tex]
where m is the mass of the object and g=9.81 m/s^2 is the acceleration of gravity, As we can see, the magnitude of this force depends only on the mass of the object: in this problem, both the objects (the piece of iron and the piece of glass) have same mass (1 kg), therefore they have same weight, and same force of gravity.
