Online Test: The Solid State | Class 12 Chemistry

Question 1 of 20

Amorphous solids are best described as:

true crystalline solids

supercooled liquids (pseudo-solids)

perfect crystals

gases at low temperature

Explanation: Amorphous solids have only short-range order and flow very slowly, so they are regarded as supercooled liquids or pseudo-solids.

Question 2 of 20

The number of atoms per unit cell in a body-centred cubic lattice is:

1

2

4

6

Explanation: $z=8\times\tfrac{1}{8}+1=2$.

Question 3 of 20

The packing efficiency of a simple cubic structure is:

52.4%

68%

74%

60%

Explanation: With $a=2r$ and $z=1$, efficiency $=\frac{\pi}{6}=52.4\%$.

Question 4 of 20

Both hcp and ccp have a coordination number of:

6

8

4

12

Explanation: In the closest packings each sphere touches 12 neighbours.

Question 5 of 20

For $N$ close-packed atoms, the number of tetrahedral voids is:

$N$

$2N$

$\tfrac{N}{2}$

$4N$

Explanation: There are $2N$ tetrahedral voids and $N$ octahedral voids.

Question 6 of 20

The density of a unit cell is given by:

$d=\frac{a^3 N_A}{zM}$

$d=\frac{zM}{a^3 N_A}$

$d=\frac{zN_A}{Ma^3}$

$d=\frac{Ma^3}{zN_A}$

Explanation: $d=\frac{zM}{a^3 N_A}$ where $z$ is atoms per cell, $M$ molar mass, $a$ edge length.

Question 7 of 20

The Schottky defect causes the density of a crystal to:

increase

decrease

remain the same

become infinite

Explanation: Equal numbers of cations and anions are removed, lowering the mass and hence the density.

Question 8 of 20

Which defect is shown by ZnS and AgBr due to the large size difference of ions?

Schottky defect

Metal excess defect

Impurity defect

Frenkel defect

Explanation: The small cation occupies an interstitial site — a Frenkel defect — favoured by a large ion-size difference.

Question 9 of 20

A face-centred cubic cell has atoms touching along the:

edge

body diagonal

none of these

face diagonal

Explanation: In fcc, atoms touch along the face diagonal, giving $\sqrt{2}\,a=4r$.

Question 10 of 20

An n-type semiconductor is produced by doping silicon with:

boron

gallium

arsenic

aluminium

Explanation: Arsenic (Group 15) donates an extra electron, giving negative (n-type) carriers.

Question 11 of 20

The total number of crystal systems and Bravais lattices respectively is:

14 and 7

4 and 14

7 and 4

7 and 14

Explanation: There are 7 crystal systems and 14 Bravais lattices.

Question 12 of 20

Colour in NaCl crystals heated in sodium vapour is due to:

Schottky defects

Frenkel defects

F-centres

impurity ions

Explanation: Electrons trapped in anion vacancies (F-centres) absorb visible light, colouring the crystal yellow.

Question 13 of 20

Which of the following is a covalent (network) solid?

Dry ice

Silicon carbide ($\text{SiC}$)

Sodium chloride

Copper

Explanation: $\text{SiC}$ is held together by a continuous covalent network, like diamond.

Question 14 of 20

A particle at the face centre of a unit cell is shared by:

8 cells

4 cells

2 cells

1 cell

Explanation: A face is shared by 2 unit cells, so a face particle contributes $\tfrac{1}{2}$.

Question 15 of 20

$\text{O}_2$ is attracted weakly by a magnetic field. It is therefore:

diamagnetic

paramagnetic

ferromagnetic

antiferromagnetic

Explanation: $\text{O}_2$ has unpaired electrons and is weakly attracted, so it is paramagnetic.

Question 16 of 20

A metal (M = 56 g/mol) crystallises in bcc with $a=2.86\times10^{-8}\ \text{cm}$. Its approximate density is:

$7.9\ \text{g cm}^{-3}$

$3.9\ \text{g cm}^{-3}$

$15.8\ \text{g cm}^{-3}$

$1.0\ \text{g cm}^{-3}$

Explanation: $d=\frac{2\times56}{(2.86\times10^{-8})^3\times6.022\times10^{23}}\approx7.9\ \text{g cm}^{-3}$.

Question 17 of 20

The radius ratio $r/R$ for a tetrahedral void is:

0.155

0.225

0.414

0.732

Explanation: A tetrahedral void (4 surrounding spheres) has a limiting radius ratio of 0.225.

Question 18 of 20

Antiferromagnetic substances such as MnO have a net magnetic moment of:

very large

small but non-zero

zero

infinite

Explanation: Equal and oppositely aligned domains cancel exactly, giving zero net magnetic moment.

Question 19 of 20

When $\text{SrCl}_2$ is added to NaCl, the number of cation vacancies created per $\text{Sr}^{2+}$ ion is:

0

1

2

3

Explanation: One $\text{Sr}^{2+}$ replaces two $\text{Na}^+$; it occupies one site and leaves one cation vacancy.

Question 20 of 20

The most efficient packing of identical spheres occupies what fraction of space?

52.4%

68%

74%

100%

Explanation: Both ccp/fcc and hcp achieve the maximum packing efficiency of 74%.

Online Test — The Solid State