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Spheres of unit diameter are centered at (𝑙 𝑚 𝑛) where 𝑙 𝑚 and l take every possible integer values.
The distance between two spheres is computed from the center of one sphere to the center of the other sphere. For a given sphere, x is the distance to its nearest sphere and y is the distance to its next nearest sphere. The value of 
is:
2
Given a sphere of unit diameter, centered at 
Diameter 
given, however let assume radius 
Distance between centres of two adjacent spheres,
The possibilities of nearest spheres: 
or 
or 
Now, the next nearest sphere lies diagonally, when centre differ by 
or 
or 
Option (c) is correct.