Density as you should know is equal to mass/volume. Solve for the volume.
Now, you know that you are dealing with a sphere. You know the volume of a sphere is V= 4/3pi r ^3.
You know the volume so just solve for r
Answer:
2.75M
Explanation:
Concentration(M)= mol/volume
0.0688mol/0.250L
=0.2752M