The fraction of total volume occupied by the atoms present in a simple cube is

\(\frac{\pi}{3\sqrt{2}}\)
\(\frac{\pi}{4\sqrt{2}}\)
\(\frac{\pi}{4}\)
\(\frac{\pi}{6}\)

Solution

If NaCl is doped with 10^-4 mol %of SrCl₂, the concentration of cation vacancies will be (NA= 6.02 × 10²³ mol^-1)

6.02 × 10¹⁶mol^-1
6.02 × 10¹⁷mol^-1
6.02 × 10¹⁴ mol^-1
6.02 × 10¹⁵ mol^-1

Solution

What is the coordination number of sodium in Na₂O?

Solution

In Na₂O there is antifluorite structure. Here negative ions form the ccp arrangement so that each positive ion is surrounded by 4 negative ions and each negative ion is surrounded by 8 positive ions. So coordination no.of Na⁺ is 4.

Which defect causes decrease in the density of crystal

Frenkel
Schottky
Interstitial
F – centre

Solution

More is the Schottky defect in crystal more is the decrease in density.

Schottky defect generally appears in :

NaCl
KCl
CsCl
all of these

Solution

Schottky defect occurs in ionic crystals of type A+B,when equal number of cations and anions are missing from their lattice sites so that the electrical neutrality is maintained. This defect generally appears in highly ionic compounds which have high coordination number.NaCl, KCl and CsCl all have high coordination numbers i.e., 6, 6 and 8 respectively. So, Schottky defect appear in all of the given compounds.

Solution

When equal number of cations (Na⁺) and anions (Cl^-) are missing from their regular lattice positions, we haves chottky defect.

The crystal system of a compound with unit cell dimensions”a= 0.387, b= 0.387 and c= 0.504 nm and ? = ? = 90° and ?= 120°” is

cubic
hexagonal
orthorhombic
rhombohedra

Solution

a = b ≠ c,? = ? = 90° and ?= 120°
These are the characteristics of a hexagonal system.

The appearance of colour in solid alkali metal halides is generally due to

Schottky defect
Frenkel defect
Interstitial positions
F-centre

Solution

The appearance of colour in solid alkali metal halide is due to presence of F-centre found as defect in the crystal structure.

Schottky defect in crystals is observed when

an ion leaves its normal site and occupies aninterstitial site
unequal number of cations and anions are missing from the lattice
density of the crystal increases
equal number of cations and anions are missing from the lattice

Solution

If in an ionic crystal of the type A⁺, B^-, equal number of cations and anions are missing from their lattice sites so that the electrical neutrality is maintained. The defect is called Schottky defect.

If Z is the number of atoms in the unit cell that represents the closest packing sequence ….. ABC ABC ……, the number of tetrahedral voids in the unit cell is equal to :

Solution

In cubic closed pack system (CCP system) .......ABC
ABC....... type of arrangement of layers is found. In this system, there are atoms at the corners as well as centre of the unit cell
∴ No. of atoms per unit cell = 8 × \(\frac{1}{8}\) + 1 = 2
Hence, the no. of tetrahedral voids in a unit cell = 2Z

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