What is the density of lithium metal (in g/cm3) if a cube measuring 0.82 cm × 1.45 cm × 1.25 cm has a mass of 0.794 g?

Density is given by mass divided by the volume of a substance.
In this case the mass is 0.794 g and the volume is 0.82 cm ×1.45 cm ×1.25 cm = 1.48625 cm³. 
Therefore, density = 0.794/ 1.48625
                              = 0.5342 g/cm³
 Thus, the density of lithium metal is 0.5342 g/cm³

First, determine the volume of the rectangular prism by multiplying its base, height, and width. That is,

   Volume = Height x weight x length

Substituting the known values,

     Volume = (0.82 cm)(1.45 cm)(1.25 cm) = 1.48625 cm³. 

For calculation of the density, we divide the given mass by the total volume.
    Density = 0.794 g/1.48625 cm³.

0.534 g/cm³

They are all full and don't need any more electrons in there outer shell.

Hope the image of the frequency formula