61.

The cubic unit cell of a metal (molar mass = 63.55g mol^-1) has an edge length of 362 pm. Its density is 8.92g cm^-3. The type of unit cell is

• primitive

• face centred

• body centred

• end centred

The number of unit cells present in 39 g of potassium if it crystallizes as body centred cube is (N = Avogadro number, At. wt. of potassium = 39)

• $\frac{\mathrm{N}}{4}$

• $\frac{\mathrm{N}}{2}$

• $\frac{\mathrm{N}}{3}$

• N

The number of octahedral and tetrahedral holes respectively present in a hexagonal close packed (hcp) crystal of 'X' atoms are

• X, 2X

• X, X

• 2X, X

• 2X, 2X

Which one of the following elements, when present as an impurity in silicon makes it a p-type semiconductor?

• As

• P

• In

• Sb

Structure of NaCl crystal is

• tetragonal

• cubic

• orthorhombic

• monoclinic

Bravais lattices are of

• 8 types

• 12 types

• 14 types

• 9 types

Point defects are present in

• ionic solids

• molecular solids

• amorphous solids

• liquids

An element has a body centered cubic structure with a unit cell edge length of 400 pm. Atomic mass of an element is 24 g mol^-1. What is the ·density of the element? (N_A = 6 × 10²³ mol^-1)

• 2.50 g cm^-3

• 1.80 g cm^-3

• 3.60 g cm^-3

• 1.25g cm^-3

The number of octahedral sites per sphere arranged in a face centred cubic structure, is

• 1

• 2

• 3

• 4

Which one of the following has Frenkel defect?

• sodium chloride

• Graphite

• Siliver Bromide

• Diamond