Assuming you really mean 1 g/ml (which is very high), then ...
convert 1 gm/ml to mg/liter to get ppm1 g = 1000 mg
1 ml = 0.001 L
1000 mg/0.001 L = 1,000,000 mg/L = 1,000,000 ppm
If diet soda has a greater density than water, it's not by much. The air in the bottle should be enough to keep it afloat. If you try to float it without the bottle, it will mix with the water.
Corrected question: http://wiki.answers.com/Q/The_density_of_h2o_is_at_4c_is_1gml_what_is_the_density_in_kgL Water has the density of 1000 kg/m3 = 1000 g/L = 1 kg/dm3 = 1 kg/L = 1 g/cm3 = 1 g/mL.
The density of an object is calculated using the formula: density = mass / volume. The volume of the cube is calculated by V = length x width x height. After calculating the volume and density, compare the object's density with the density of water (1 g/mL). If the object's density is greater than the water's density, it will sink. If the object's density is less than the water's density, it will float.