Please refer to The Solid State Class 12 Chemistry Important Questions with answers below. These solved questions for Chapter 1 The Solid State in NCERT Book for Class 12 Chemistry have been prepared based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these solved problems properly as these will help them to get better marks in your class tests and examinations. You will also be able to understand how to write answers properly. Revise these questions and answers regularly. We have provided Notes for Class 12 Chemistry for all chapters in your textbooks.

Important Questions Class 12 Chemistry Chapter 1 The Solid State

All The Solid State Class 12 Chemistry Important Questions provided below have been prepared by expert teachers of Standard 12 Chemistry. Please learn them and let us know if you have any questions.

Very Short Answer Questions :

Question. Write a feature which will distinguish a metallic solid from an ionic solid.
Answer : (i) Metallic solids are malleable and ductile whereas ionic solids are hard and brittle.
(ii) In solid state, ionic solids are electrical insulators because ions are not free to move about, e.g. NaCl, Na₂SO₄, etc. while metals are good electrical conductors in solid state because of the presence of free electrons e.g. copper, nickel etc. (any one)

Question. How will you distinguish between the following pair of terms :
Tetrahedral and octahedral voids?
Answer : A void surrounded by four atoms whose centre when joined forms tetrahedron is tetrahedral void.
Number of tetrahedral voids = 2 × Number of atoms.
A void surrounded by six atoms whose centre when joined forms an octahedron is called octahedral voids.
Number of octahedral voids = Number of atoms.

Question. How may the conductivity of an intrinsic semiconductor be increased?
Answer : The conductivity of intrinsic semiconductor like silicon is too low to be of practical use. This conductivity is increased by adding an appropriate amount of suitable impurity like Al or As which is electron deficient or electron rich. So, the electrical conductivity of silicon is increased.

Question. Write the type of magnetism observed when the magnetic moments are oppositely aligned and cancel out each other.
Answer : Antiferromagnetism

Question. Give an example of an ionic compound which shows Frenkel defect.
Answer : Frenkel defect is shown by ionic solids in which difference in size of cations and anions is large.
Examples : ZnS, AgI and AgBr.

Question. Which point defect of its crystals decreases the density of a solid?
Answer : Schottky defect.

Question. Define the following term :
Molarity (M)
Answer : Molarity : It is the number of moles of the solute dissolved per litre of the solution. It is denoted by M.
∴ Molarity = Moles of solute/Volume of solution in litre

Question. Which stoichiometric defect in crystals increases the density of a solid?
Answer : Interstitial defect

Question. How many atoms constitute one unit cell of a face-centred cubic crystal?
Answer : In face centred cubic unit cell
(i) No. of atoms contributed from the corners of the unit cell
= 8 corner atoms × 1/8 atom per unit cell
= 8 × 1/8 = 1 atom
(ii) No. of atoms contributed from the faces
= 6 face centred atoms × 1/2 atoms per unit cell
= 6 x  1/2 = 3 atoms
∴ Total no. of atoms per unit cell = 4 atoms

Question. Impurity doped silicon is a semiconductor.
Answer : The conductivity of intrinsic semiconductor like silicon is too low to be of practical use. This conductivity is increased by adding an appropriate amount of suitable impurity like Al or As which is electron deficient or electron rich. So, the electrical conductivity of silicon is increased.

Question. Why is Frenkel defects not found in pure alkali metal halides?
Answer : Frenkel defects is not found in alkali metal halides because the ions cannot get into the interstitial sites due to their larger size.

Question. Define the following term :
Ferromagnetism 
Answer : Ferromagnetism : Materials which are strongly attracted by magnetic field are called ferromagnetic materials and the property thus exhibited is caused ferromagnetism.
e.g., Fe, Co, Ni show ferromagnetism at room temperature.

Question. What type of semiconductor is formed when silicon is doped with As?
Answer : n-type semiconductor is formed when silicon is doped with arsenic.

Question. Assign reason for the following :
Phosphorus doped silicon is a semiconductor.
Answer : Phosphorus is pentavalent. When phosphorus is doped in silicon it increases the number of electrons which increases the conductivity of doped silicon and makes it semiconductor.

Question. Calculate the number of atoms in a face centred cubic unit cell.
Answer : In face centred cubic unit cell
(i) No. of atoms contributed from the corners of the unit cell
= 8 corner atoms × 1/8 atom per unit cell
= 8 × 1/8 = 1 atom
(ii) No. of atoms contributed from the faces
= 6 face centred atoms × 1/2 atoms per unit cell
= 6 x  1/2 = 3 atoms
∴ Total no. of atoms per unit cell = 4 atoms

Question. Define the following term :
Molality (m) 
Answer : Molality (m) is defined as the number of moles of the solute per kilogram of the slovent and  is expressed as :
Molality (m) = Molesofsolute/Mass of solvent (in kg)

Question. What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 2/3^rd of octahedral voids?
Answer : No. of Y atoms per unit cell in ccp lattice = 1/8 x 8 + 1/2 x 6 + 4
[∴ ccp is same as face-centred cubic packing. Thus, no. of atoms = 4]
No. of octahedral voids = No. of atoms present in ccp lattice
No. of octahedral voids occupied by atoms = 2/3 × 4 = 8/3
Therefore, formula of the compound = X_8/3Y₄ = X₂Y₃

Question. Assign reason for the following :
Some of the very old glass objects appear slightly milky instead of being transparent.
Answer : Some of the glass objects from ancient monuments look milky instead of being transparent because it undergoes heating during the day and cooling at night i.e., annealing over a number of years.
As a result, it acquires some crystalline character. They become a bit opaque

Question. Define the following term :
Ideal solution
Answer : A solution which obeys Raoult’s law of vapour pressure for all compositions is called ideal solution.
In this solution ΔV_mix = 0, ΔH_mix = 0
A ……. B interaction = A ….. A and B ….. B interactions.

Question. What type of substances would make better magnets, ferromagnetic or ferrimagnetic?
Answer : Ferromagnetic substances because these substances become a permanent magnet.

Question. What type of defect can arise when a solid is heated?
Answer : On heating a solid vacancy defect is produced in the crystal. This is because on heating, some lattice sites become vacant.

Question. What type of semiconductor is obtained when silicon is doped with boron?
Answer : p-type semiconductor is obtained when silicon is doped with boron.

Question. What type of magnetism is shown in the following alignment of magnetic moments?
Answer : Ferromagnetism

Short Answer Questions :

Question. The density of copper is 8.95 g cm^–3. It has a face centred cubic structure. What is the radius of copper atom? (Atomic mass Cu = 63.5 g mol^–1, N_A = 6.02 × 10²³ mol^–1)
Answer : 

Question. Silver crystallises with face-centred cubic unit cell. Each side of this unit cell has a length of 409 pm. What is the radius of silver atom?
Assume the atoms just touch each other on the diagonal across the face of the unit cell.
Answer :  As the atoms just touch each other on the diagonal across the face of unit cell, therefore

Question. Iron has a body centred cubic unit cell with a cell dimension of 286.65 pm. The density of iron is 7.87 g cm^–3. Use this information to calculate Avogadro’s number.
(Gram atomic mass of Fe = 56 g mol^–1).
Answer : 

Question. Silver crystallises in fcc lattice. If the edge length of the unit cell is 4.077 × 10^–8cm and density of the crystal is 10.5 g cm^–3, calculate the atomic mass of silver.
(N_A = 6.02 × 10²³ atoms mol^–1)
Answer : Given, edge length a = 4.077 × 10^–8 cm
density d = 10.5 g cm^–3
For fcc lattice Z = 4, Atomic mass M = ?
Using formula d = Z x M/N_A x a³
or,  M = d x N_A x a³/Z
or  M = 10.5 g cm^-3 6.022×10²³ atoms mol^-1 x (4.077 x 10^-8 cm)³/ 4 atoms
or M = 107.12 g mol^–1

Question. (i) What type of non-stoichiometric point defect is responsible for the pink colour of LiCl?
(ii) What type of stoichiometric defect is shown by NaCl?
Answer : (i) Metal excess defect is responsible for pink colour of LiCl. It is also known as anion vacancy defect.
(ii) NaCl crystal shows Schottky defect.

Question. An element crystallises in a bcc lattice with cell edge of 500 pm. The density of the element is 7.5 g cm^–3. How many atoms are present in 300 g of the element? 
Answer : 

Question. Express the relationship between atomic radius (r) and the edge length (a) in the bcc unit cell.
Answer : In bcc unit cell r = √3/4 a

Question. An element occurs in bcc structure. It has a cell edge length of 250 pm. Calculate the molar mass if its density is 8.55 g cm^–3. Also calculate the radius of an atom of this element.
Answer : 

Question. How would you account for the following?
(a) Frenkel defects are not found in alkali metal halides.
(b) Schottky defects lower the density of related solids. 
Answer : (a) Frenkel defects is not found in alkali metal halides because the ions cannot get into the interstitial sites due to their larger size.
(b) Schottky defects occur when cations and anions are missing from their lattice site. Mass of unit cell decreases which decreases the density of the solid.

Question. The density of copper metal is 8.95 g cm^–3. If the radius of copper atom be 127.8 pm, is the copper unit cell simple cubic, body-centred cubic or face-centred cubic?
(Given : atomic mass of Cu = 63.54 g mol^–1 and N_A = 6.02 × 10²³ mol^–1)
Answer : 

Question. If NaCl is doped with 10^–3 mole percen SrCl₂, what will be the concentration of cation vacancies? (N_A = 6.02 × 10²³ mol^–1) 
Answer : The number of cation vacancies created in the lattice of NaCl is equal to the number of divalent Sr²⁺ ions added.
Concentration of Sr²⁺ = 10^–3 mol%
= 10⁻³/100 = 10^-5 mol
1 mole of Sr²⁺    = 6.023 × 10²³Sr²⁺ ions
10^–5 mol of Sr²⁺ = 6.023 × 10²³ × 10^–5
                         = 6.023 × 10¹⁸ Sr²⁺ ions.
Hence, the concentration of cation vacancies is 6.023 × 10¹⁸.

Question. Explain the following terms with one suitable example of each.
(a) Ferromagnetism
(b) Paramagnetism
Answer : (a) Ferromagnetism : Substances which are very strongly attracted by the magnetic field are called ferromagnetic and this property is called ferromagnetism.
Examples : Iron, cobalt, nickel, gadolinium and CrO₂.
These substances can be permanently magnetised i.e., they retain magnetic property even in absence of applied magnetic field.
In ferromagnetic substance all the domains (tiny magnet formed by grouping of metal ions in small region) are oriented in the direction of the applied magnetic field and produce a strong magnetic effect. This ordered orientation of domain persists even when the magnetic field is removed.
Ferrimagnetism : Substances which are weakly attracted by the magnetic field as compared to ferromagnetic substances are called ferrimagnetic and this property is called ferrimagnetism.
Examples : Fe₃O₄ (Magnetite, Ferrites – MgFe₂O₄,ZnFe₂O₄.
Ferrimagnetism is observed when the magnetic domains are aligned in parallel and antiparallel directions in unequal numbers. Hence, net magnetic moment is never zero.
These substances lose ferrimagnetism and become paramagnetic on heating.

Schematic alignment of magnetic moments in
(a) ferromagnetic (b) ferrimagnetic.
(b) Paramagnetism : Materials which are weakly attracted by magnetic fields are called paramagnetic materials and this property is called paramagnetism.
Paramagnetic substances contain unpaired electrons.
e.g., TiO, CuO, O₂ and VO₂, etc.

Question. Explain the following terms with suitable examples :
(i) Schottky defect
(ii) Interstitial defect
Answer : Schottky defect : The defect in which cations and anions are missing in the stoichiometric ratio of compound is called Schottky defect. Schottky defect is actually vacancy defect in ionic solids. In this defect, electrical neutrality is maintained. In this defect, density of solid decreases. Schottky defect is shown by ionic solids in which the cation and anion are of almost similar sizes.
Examples : NaCl, KCl, CsCl, AgBr, etc.
(ii) Interstitial defect : The defect in which some constituent particles occupy the interstitial site in the crystal is called interstitial defect. This defect increases density of solid. e.g., non-ionic solids.

Question. An element crystallises in a fcc lattice with cell edge of 250 pm. Calculate the density if 300 g of this element contains 2 × 10²⁴ atoms.
Answer : 

Question. Define the following term :
Colligative properties
Answer : Properties which depend upon the number of solute particles irrespective of their nature relative to the total number of particles present in the solution are called colligative properties.

Question. What are point defects? Describe two types of point defects. 
Answer : Point defects are the irregularities or deviations from ideal arrangement around a point or an atom in a crystalline solid. Types of point defects are :
Stoichiometric defects : These are the point defects that do not disturb the stoichiometry of the solid.
They are also called intrinsic or thermodynamic defects.
In non-ionic solids :
(i) Vacancy defect : Some of the lattice sites are vacant, decreases the density of the substance. 
(ii) Interstitial defect : Some constituent particles (atoms or molecules) occupy an interstitial site, increases the density of the substance.
In ionic solids :
(i) Frenkel defect or dislocation defect : The smaller ion (usually cation) is dislocated from its normal site to an interstitial site. 
It does not change the density of the solid and is shown by ionic substances in which there is a large difference in the size of ions, e.g., ZnS, AgCl, AgBr and AgI due to small size of Zn²⁺ and Ag⁺ ions.
(ii) Schottky defect : Equal number of cations and anions are missing. It decreases the density of the substance and is shown by ionic substances in which the cation and anion are of almost similar sizes e.g., NaCl, KCl, CsCl and AgBr. AgBr shows both, Frenkel as well as Schottky defects.
Non-stoichiometric defects : When the ratio of the cations to the anions becomes different from that indicated by the ideal chemical formula, the defects are called non-stoichiometric defects.
Metal excess defect :
(i) Due to anionic vacancies e.g., on heating crystals of NaCl in presence of Na vapour, some anions (Cl^–) leave lattice sites which are occupied by electrons called F-centres giving colour to crystals.
(ii) Due to presence of extra cations at interstitial sites e.g., on heating, white ZnO turns yellow as it loses oxygen and Zn²⁺ ions and the electrons occupy interstitial sites.
Metal deficiency defect : There are many solids which are diffcult to prepare in the toichiometric composition and less amount the metal as compared to the stoichiometric proportion (any two).

Question. Aluminium crystallises in a cubic close-packed structure. Radius of atom in the metal is 125 pm.
(i) What is the length of the side of the unit cell?
(ii) How many unit cells are there in 1 cm³ of aluminium?
Answer : 

Question. A 10% solution (by mass) of sucrose in water has freezing point of 269.15 K. Calculate the freezing point of 10% glucose in water, if freezing point of pure water is 273.15 K. 
(Given : Molar mass of sucrose = 342 g mol^–1, molar mass of glucose = 180 g mol^–1)
Answer : Molality (m) of sucrose solution

Question. Explain the following terms with suitable examples :
(a) Crystal defects
(b) Metal deficiency defects
Answer : (a) Point defects are the irregularities or deviations from ideal arrangement around a point or an atom in a crystalline substance, whereas the line defects are the irregularities or deviations from ideal arrangement in entire rows of lattice points. These irregularities are called crystal defects.
(b) This type of defects generally occurs when metal shows variable valency. The defect arises due to the missing of cation from its lattice site and the presence of the cation having higher charge in the adjacent lattice site, e.g., Fe_xO.