Molarity is defined as the moles of solute per liter of solution. 
. Where M is molarity, n is the number of moles and V is the volume. First we must find the molar mass of 
which is 109.98 g/mol
Then we find the molarity using above equation
a. The unit cell is the smallest group of atom which have overall symmetry of a crystal, and from which is the entire letters can be buled built up by repetition in 3 dimensions.
b. The volume(v) of the unit cell is equal to the cell edge length (a)cubed.
c. density of polonium is 9.32g/cm3.
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Here is the link to a great video that explains your question nicely, hope this helps.
The answer is 18 you multiply wavelength (6) times frequency (3)
