1.13   Niobium crystallises in body-centred cubic structure. If density is  calculate atomic radius of niobium using its atomic mass 
                
                  Here we will use the relation between density and edge length.
                                          
It is given that Niobium crystallises in body-centred cubic structure so the value of z = 2.
So we will put the value of density, molar mass and z.
We get,
                                          
or                                       
or                                       
We know the relation between the radius of the atom and edge length in bcc lattice.
                                          
we get the radius of niobium atom = 143.1 pm.