. In
this sample what fraction of metal ions are 
ions?
What type of non-stoichiometric defect is present in this sample?
Or
Niobium crystallises in body csnered cubic structure. If
density is 8.55 
.
Calculate the atomic radius of niobium using its atomic mass 93 u. [3]
Answer:
From the valency of Fe (II) and Fe (III), it is clear that
three Fe (II) ions will be replaced by two Fe (III) causing a loss of one iron
ion. [1]
Total loss of iron from one molecule of FeO
=1- 0.93 = 0.07
Thus, 
present
in one molecule of FeO
= 2 x 0. 0 7 = 0. 14 [1]
Fraction of Fe (III)
Fraction Fe (II) =1-0.15 =0.85 [1]
Or
Density is related to other parameters by equation d
(density) 
M
is atomic mass = 93 u Z = 2 for bcc structure a = edge length No =
Avogadro's number 
[1]
[1]
For bcc structure
[1]
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