JEE Chemistry The Solid State MCQs Set 15

Answer: (d) B and D are correct

Explanation:
1. Amorphous solids have only short range order in the arrangement of particles.
2. They do not have a sharp melting point; they soften over a range of temperature.
3. So statements B and D are correct.

Teacher's Note:
1. Crystalline solids have long range order and a sharp melting point.

Answer: (d) presence of free electrons

Explanation:
1. Free (delocalised) electrons absorb light and re-emit it immediately.
2. This gives metals their characteristic lustre.

Teacher's Note:
1. Free electrons also explain electrical and thermal conductivity.

Answer: (d) Sugar

Explanation:
1. Glass, rubber and plastic are amorphous solids.
2. Sugar has a regular, long range arrangement of molecules, so it is crystalline.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (c) a covalent (network) solid

Explanation:
1. Each carbon atom in diamond is bonded covalently to four other carbon atoms in a giant network.

Teacher's Note:
1. Diamond is very hard and a non-conductor.

Answer: (c) polymorphism

Explanation:
1. Existence of a substance in more than one crystalline form is polymorphism.
2. Isomorphism refers to different substances having the same crystal form.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (a) Covalent (network) solids

Explanation:
1. Melting a network solid requires breaking strong covalent bonds throughout the whole crystal.
2. Examples are diamond and silicon carbide, which melt at far higher temperatures than ionic or molecular solids.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (c) \( \ce{W} \)

Explanation:
1. Tungsten is a metal whose atoms are held by metallic bonding.
2. C and Si are covalent solids and AgCl is ionic.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (c) molecular crystals

Explanation:
1. Iodine crystals consist of discrete \( \ce{I2} \) molecules held together by weak van der Waals (London) forces.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (d) Ice

Explanation:
1. Ice consists of water molecules held by hydrogen bonds and van der Waals forces.
2. SiC and graphite are covalent solids and NaCl is ionic.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (b) \( \ce{LiF} \)

Explanation:
1. \( \ce{LiF} \) is made of \( \ce{Li+} \) and \( \ce{F-} \) ions held by electrostatic attraction.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (b) They are anisotropic

Explanation:
1. Amorphous solids are isotropic because their properties are the same in all directions.
2. So the statement that they are anisotropic is incorrect.

Teacher's Note:
1. Anisotropy is a property of crystalline solids.

Answer: (b) 14

Explanation:
1. There are 7 crystal systems.
2. Different centring (primitive, body-centred, face-centred, end-centred) gives a total of 14 Bravais lattices.

Teacher's Note:
1. 32 is the number of crystallographic point groups and 230 is the number of space groups.

Answer: (b) \( 0.414\,r \)

Explanation:
1. For an octahedral hole \( r_{hole}/r=0.414 \).
2. So the maximum radius is \( 0.414\,r \).

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (c) has 4 NaCl units

Explanation:
1. \( \ce{Cl-} \) ions occupy corners and face centres: \( 8\times\frac18+6\times\frac12=4 \).
2. The \( \ce{Na+} \) ions occupy edge centres and the body centre: \( 12\times\frac14+1=4 \).
3. So there are 4 NaCl units; the cell is neutral.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (c) \( 0.225-0.414 \)

Explanation:
1. Radius ratio 0.225 to 0.414 corresponds to coordination number 4, i.e. tetrahedral arrangement.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (a) face centred cubic

Explanation:
1. KCl has the rock salt structure: an fcc arrangement of \( \ce{Cl-} \) ions with \( \ce{K+} \) ions in the octahedral holes.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (b) minimum potential energy

Explanation:
1. Particles settle where attractive and repulsive forces balance, which is the position of minimum potential energy (maximum stability).

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (a) high lattice energy

Explanation:
1. For \( \ce{BaSO4} \) the lattice energy is high compared with the hydration energy of its ions.
2. Hence it does not dissolve appreciably.

Teacher's Note:
1. A salt is soluble when hydration energy exceeds lattice energy.

Answer: (d) \( 0.732-1.000 \)

Explanation:
1. CsCl structure has coordination number 8 (cubic).
2. Radius ratio for coordination number 8 lies between 0.732 and 1.000.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (c) \( \ce{CuCl} \)

Explanation:
1. CuCl has an fcc lattice of \( \ce{Cl-} \) with \( \ce{Cu+} \) in alternate tetrahedral holes, the same as ZnS.
2. AgCl and NaCl are rock salt type and TlCl is CsCl type.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (d) antifluorite

Explanation:
1. Oxide ions form an fcc lattice and sodium ions fill all the tetrahedral holes.
2. This is the reverse of the fluorite arrangement, so it is antifluorite.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (b) hexagonal

Explanation:
1. a = b \( \neq \) c with \( \alpha=\beta=90^\circ \) and \( \gamma=120^\circ \) is the hexagonal system.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (c) 8

Explanation:
1. An fcc unit cell contains 4 atoms.
2. Tetrahedral voids = 2 \( \times \) 4 = 8.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.

Answer: (d) 4

Explanation:
1. \( 8\times\frac18+6\times\frac12=4 \) atoms.

Teacher's Note:
1. Identify the key concept in the question first, then apply the standard relation step by step.
2. Check units and the number of significant figures before choosing the option.