Schottky defects occurs mainly in electrovalent compounds where

• positive ions and negative ions are of different size

• positive ions and negative ions are of same size

• positive ions are small and negative ions are big

• positive ions are big and negative ions are small

An ion leaves its regular site occupy a position in the space between the lattice sites is called

• Frenkel defect

• Schottky defect

• impurity defect

• vacancy defect

The 8: 8 type of packing is present in

• MgF₂

• CsCl

• KCl

• NaCl

A metallic element has a cubic lattice. Each edge of the unit cell is 2 $\stackrel{°}{\mathrm{A}}$. The density of the metal is 2.5 g cm ^-3 . The unit cells in 200 g of metal are

• $1 \times {10}^{24}$

• $1 \times {10}^{20}$

• $1 \times {10}^{22}$

• 1 $1 \times {10}^{25}$

Which among the following solids crystallises as a face centred cube?

• Iron

• Rubidium

• Uranium

• Platinum

Which metal among the following has the highest packing efficiency?

• Iron

• Tungsten

• Aluminium

• Polonium

Which metal crystallises in a simple cubic structure?

• Polonium

• Copper

• Nickel

• Iron

An element crystallising in body centred cubic lattice has an edge length of 500 pm. If its density is 4 g cm^-3, the atomic mass of the element (in g mol^-1) is (consider N_A = 6 × 10²³)

• 100

• 250

• 125

• 150

39.

Aluminium (atomic mass = 27) crystallises in a cubic system with edge length of 4 Å. Its density is 2. 7 g cm^-3 The number of aluminium atoms present per unit cell is

• 5

• 6

• 4

• 2

For two isomorphous crystals A and B, the ratio of density of A to that of B is 1.6 while the ratio of the edge length of B to that of A is 2. If the molar mass of crystal B is 200 g mol^-1, then that of crystal A is

• 240 g mol^-1

• 40 g mol^-1

• 80 g mol^-1

• 160 g mol^-1