VITEEE 2017 Paper

Following generalization can be easily derived for various types of lattice arrangements in cubic cells between the edge length (a) of the cell and r the radius of the sphere.
For simple cubic : a = 2r or r =

a

2

For body centred cubic :
a =

4

√3

r or r =

√3

4

a
For face centred cubic :
a = 2√2r or r =

1

2√2

a
Thus the ratio of radii of spheres for these will be simple: bcc: fcc
=

1

2

a :

√3

4

a :

1

2√2

a
option (a) is correct answer.