If ‘a’ stands for the edge length of the cubic systems: simple cubic, body centred cubic and face centred cubic, then the ratio of radii of the spheres in these system will be respectively. [CBSE AIPMT 2008]

For the simple cubic: ' 2 a r r Here a = edge length and interatomic distance. For the body centered ' 2 2 a r r Therefore the ratio of radii of the three will be 3 : : 2 4 2 2 a a a Hence the correct answer is option (a) 8. Which of the following statements is not correct? [CBSE AIPMT 2008] (a) The fraction of the total volume occupied by the atoms in a primitive cell is 0.48. (b) Molecular solids are generally volatile. (c) The number of carbon atoms in a unit cell of diamond is 4. (d) The number of Bravais lattices in which a crystal can be categorised is 14. The diamond has