We are given the length, the mass and the density of the cylinder. First let us calculate for the volume by dividing the mass by the density.
 volume = mass /density
 where mass = 2.17 kg = 2170 g, therefore:
 volume = 2170 g / (2.33 g/cm^3)
 volume = 931.33 cm^3
  
 We know that the volume of a cylinder has the formula:
 volume = π r^2 h
 since h = 16.8 cm, therefore calculating for radius:
 931.33 cm^3 = π r^2 (16.8 cm)
 r^2 = 17.646 cm^2
 r = 4.2 cm
  
 Hence the diameter (d) is:
 d = 2 r
 d = 8.4 cm