40 Multiple Choice Questions on The Solid State for NEET/JEE Mains

Each question has four options, with only one correct answer. Detailed explanations are provided for each question.

Question 1: Which of the following statements is incorrect about amorphous solids? (A) They soften over a range of temperatures. (B) They are anisotropic. (C) They are considered supercooled liquids. (D) They have only short-range order.

Explanation 1:

• Correct Answer: (B)
• Reasoning: Amorphous solids are isotropic, meaning their physical properties are the same in all directions due to their random arrangement of particles. Anisotropy is a characteristic of crystalline solids.

Question 2: Which of the following is an example of a covalent or network solid? (A) Dry ice (CO2​) (B) Silicon carbide (SiC) (C) Zinc sulphide (ZnS) (D) Copper (Cu)

Explanation 2:

• Correct Answer: (B)
• Reasoning: Covalent solids are characterized by a continuous network of covalent bonds. SiC (Silicon Carbide) forms a 3D network of covalently bonded atoms. Dry ice is a molecular solid, ZnS is an ionic solid, and Copper is a metallic solid.

Question 3: What is the coordination number of an atom in a Body-Centered Cubic (BCC) lattice? (A) 6 (B) 8 (C) 10 (D) 12

Explanation 3:

• Correct Answer: (B)
• Reasoning: In a BCC lattice, the central atom is in contact with the 8 atoms present at the corners of the unit cell, hence its coordination number is 8.

Question 4: How many atoms are effectively present in a Face-Centered Cubic (FCC) unit cell? (A) 1 (B) 2 (C) 3 (D) 4

Explanation 4:

• Correct Answer: (D)
• Reasoning: In an FCC unit cell, there are 8 atoms at the corners (each contributing 1/8) and 6 atoms at the face centers (each contributing 1/2). So, effective atoms = (8×1/8)+(6×1/2)=1+3=4.

Question 5: Which type of defect is responsible for the yellow color of NaCl crystals when heated in sodium vapor? (A) Schottky defect (B) Frenkel defect (C) Metal excess defect (anion vacancies/F-centers) (D) Metal deficiency defect

Explanation 5:

• Correct Answer: (C)
• Reasoning: Heating NaCl in sodium vapor causes excess sodium atoms to deposit on the surface. Cl- ions diffuse to the surface to combine with Na atoms, leaving behind anion vacancies in the crystal. Electrons (from Na atoms) then occupy these vacancies, forming F-centers, which absorb light and impart color.

Question 6: Which of the following is a characteristic property of ionic solids? (A) Low melting point (B) Good electrical conductors in solid state (C) Hard and brittle (D) Malleable and ductile

Explanation 6:

• Correct Answer: (C)
• Reasoning: Ionic solids are held by strong electrostatic forces, making them hard. However, repulsion between like-charged ions upon displacement makes them brittle. They have high melting points and are insulators in the solid state. Malleability and ductility are properties of metals.

Question 7: What is the packing efficiency of a simple cubic (SC) lattice? (A) 74% (B) 68% (C) 52.4% (D) 47.6%

Explanation 7:

• Correct Answer: (C)
• Reasoning: The packing efficiency of a simple cubic lattice is 52.4%. FCC and HCP have 74%, and BCC has 68%.

Question 8: The radius ratio for an octahedral void is: (A) 0.155R (B) 0.225R (C) 0.414R (D) 0.732R

Explanation 8:

• Correct Answer: (C)
• Reasoning: The radius ratio (rvoid​/Rsphere​) for an octahedral void is 0.414. 0.225 is for tetrahedral, 0.732 for cubic, and 0.155 for triangular.

Question 9: A substance has an FCC structure. If the edge length of its unit cell is ‘a’, what is the relation between ‘a’ and the atomic radius ‘r’? (A) a=2r (B) a=3​4r​ (C) a=22​r (D) a=4r

Explanation 9:

• Correct Answer: (C)
• Reasoning: In an FCC lattice, atoms touch along the face diagonal. The length of the face diagonal is 4r. By Pythagorean theorem, face diagonal =a2+a2​=2a2​=a2​. So, 4r=a2​, which means a=2​4r​=22​r.

Question 10: Which of the following is an example of an n-type semiconductor? (A) Pure Silicon (B) Silicon doped with Boron (C) Germanium doped with Arsenic (D) Silicon doped with Gallium

Explanation 10:

• Correct Answer: (C)
• Reasoning: n-type semiconductors are formed by doping a Group 14 element (Si, Ge) with a Group 15 element (P, As, Sb). Arsenic (As) is a Group 15 element. Boron (B) and Gallium (Ga) are Group 13 elements, which form p-type semiconductors. Pure silicon is an intrinsic semiconductor.

Question 11: What happens to the density of a crystal in the presence of a Schottky defect? (A) Increases (B) Decreases (C) Remains unchanged (D) First increases then decreases

Explanation 11:

• Correct Answer: (B)
• Reasoning: In a Schottky defect, an equal number of cations and anions are missing from the crystal lattice. This means mass is lost from the crystal while its volume remains essentially the same, leading to a decrease in overall density.

Question 12: Which crystal system has a=b=c and α=β=γ=90∘? (A) Cubic (B) Tetragonal (C) Orthorhombic (D) Monoclinic

Explanation 12:

• Correct Answer: (C)
• Reasoning: This description matches the Orthorhombic crystal system. Cubic has a=b=c, Tetragonal has a=b=c, and Monoclinic has one angle not equal to 90∘ (β=90∘).

Question 13: The number of tetrahedral voids per atom in a close-packed structure is: (A) 1 (B) 2 (C) 3 (D) 4

Explanation 13:

• Correct Answer: (B)
• Reasoning: In any close-packed structure (HCP or CCP/FCC), the number of tetrahedral voids is twice the number of effective atoms (N) in the unit cell. So, it’s 2N voids for N atoms, meaning 2 voids per atom.

Question 14: Which of the following is a diamagnetic substance? (A) O2​ (B) Fe3+ (C) NaCl (D) Cu2+

Explanation 14:

• Correct Answer: (C)
• Reasoning: Diamagnetic substances have all paired electrons and are weakly repelled by a magnetic field. NaCl consists of Na+ and Cl− ions, both of which have completely filled electron shells (all electrons paired). O2​, Fe3+, and Cu2+ all have unpaired electrons and are paramagnetic.

Question 15: Which type of solid is generally very hard, has a very high melting point, and is a poor electrical conductor (insulator)? (A) Molecular solid (B) Ionic solid (C) Metallic solid (D) Covalent/Network solid

Explanation 15:

• Correct Answer: (D)
• Reasoning: Covalent or network solids like Diamond or Silicon Carbide are characterized by strong covalent bonds extending throughout the entire structure, leading to extreme hardness, very high melting points, and poor conductivity.

Question 16: If the radius of an atom forming an FCC lattice is ‘r’, the length of the body diagonal of the unit cell is: (A) 2r (B) 22​r (C) 4r (D) 3​×(22​r)

Explanation 16:

• Correct Answer: (D)
• Reasoning: In an FCC lattice, the edge length ‘a’ is related to the atomic radius ‘r’ by a=22​r. The body diagonal of a cube is 3​a. Substituting ‘a’, the body diagonal =3​×(22​r). (Note: Atoms don’t touch along the body diagonal in FCC).

Question 17: An element crystallizes in a simple cubic lattice. If its atomic radius is ‘r’, what is the edge length ‘a’ of the unit cell? (A) r (B) 2r (C) 2​r (D) 4r

Explanation 17:

• Correct Answer: (B)
• Reasoning: In a simple cubic lattice, atoms are at the corners and touch each other along the edges. Therefore, the edge length ‘a’ is equal to twice the atomic radius, i.e., a=2r.

Question 18: Which of the following crystal systems has all axial lengths unequal and all axial angles unequal and not equal to 90∘? (A) Monoclinic (B) Rhombohedral (C) Triclinic (D) Orthorhombic

Explanation 18:

• Correct Answer: (C)
• Reasoning: This description perfectly matches the Triclinic crystal system (a=b=c, α=β=γ=90∘).

Question 19: What is the percentage of empty space in a Body-Centered Cubic (BCC) structure? (A) 26% (B) 32% (C) 48% (D) 68%

Explanation 19:

• Correct Answer: (B)
• Reasoning: The packing efficiency of a BCC structure is 68%. Therefore, the percentage of empty space (voids) is 100%−68%=32%.

Question 20: Fe3​O4​ is an example of a: (A) Ferromagnetic substance (B) Antiferromagnetic substance (C) Ferrimagnetic substance (D) Paramagnetic substance

Explanation 20:

• Correct Answer: (C)
• Reasoning: Fe3​O4​ (magnetite) is a ferrite, which is a classic example of a ferrimagnetic substance. In ferrimagnetic materials, the magnetic moments are aligned in parallel and anti-parallel directions in unequal numbers, resulting in a net magnetic moment.

Question 21: Which type of molecular solid is generally harder due to the presence of stronger intermolecular forces? (A) Non-polar (B) Polar (C) Hydrogen-bonded (D) All are equally soft

Explanation 21:

• Correct Answer: (C)
• Reasoning: Hydrogen bonds are significantly stronger than London dispersion forces and dipole-dipole interactions. Therefore, hydrogen-bonded molecular solids (like ice) are relatively harder and have higher melting points compared to non-polar and polar molecular solids.

Question 22: In a close-packed structure, if the number of octahedral voids is ‘N’, the number of tetrahedral voids will be: (A) N/2 (B) N (C) 2N (D) 4N

Explanation 22:

• Correct Answer: (C)
• Reasoning: For a given number of close-packed spheres, if there are ‘N’ octahedral voids, there will be 2N tetrahedral voids.

Question 23: Which of the following defects is characterized by the displacement of an ion from its lattice site to an interstitial site? (A) Schottky defect (B) Frenkel defect (C) Vacancy defect (D) Impurity defect

Explanation 23:

• Correct Answer: (B)
• Reasoning: This is the definition of a Frenkel defect. A Schottky defect involves missing ions, a vacancy defect involves a missing particle in a non-ionic solid, and an impurity defect involves a foreign atom.

Question 24: The correct order of packing efficiency in different types of cubic unit cells is: (A) SC > BCC > FCC (B) FCC > BCC > SC (C) BCC > FCC > SC (D) SC > FCC > BCC

Explanation 24:

• Correct Answer: (B)
• Reasoning: The packing efficiencies are: FCC (74%) > BCC (68%) > SC (52.4%).

Question 25: Which of the following increases the electrical conductivity of a semiconductor? (A) Decreasing temperature (B) Increasing temperature (C) Keeping it pure (D) Decreasing doping concentration

Explanation 25:

• Correct Answer: (B)
• Reasoning: Semiconductors have a small band gap. Increasing temperature provides more thermal energy, allowing more electrons to jump from the valence band to the conduction band, thus increasing conductivity. Doping also increases conductivity, but increasing temperature is a direct way to increase conductivity for both intrinsic and extrinsic semiconductors.

Question 26: The value of Z (number of atoms per unit cell) for an element crystallizing in a primitive cubic unit cell is: (A) 1 (B) 2 (C) 4 (D) 6

Explanation 26:

• Correct Answer: (A)
• Reasoning: In a primitive (simple) cubic unit cell, atoms are present only at the 8 corners. Each corner atom contributes 1/8 to the unit cell. So, Z=8×(1/8)=1.

Question 27: A compound forms a hexagonal close-packed (HCP) structure. The coordination number of each atom in this structure is: (A) 6 (B) 8 (C) 10 (D) 12

Explanation 27:

• Correct Answer: (D)
• Reasoning: Both HCP and CCP (FCC) structures are highly efficient close-packed structures where each atom has 12 nearest neighbors (6 in its own layer, 3 above, and 3 below).

Question 28: Which of the following statements is true for an amorphous solid? (A) They have a definite heat of fusion. (B) They are anisotropic. (C) They exhibit a sharp melting point. (D) They flow very slowly like supercooled liquids.

Explanation 28:

• Correct Answer: (D)
• Reasoning: Amorphous solids are sometimes called supercooled liquids because they have a tendency to flow, albeit very slowly, over time. The other options describe crystalline solids.

Question 29: Doping Silicon with a Group 13 element like Boron creates: (A) n-type semiconductor (B) p-type semiconductor (C) Intrinsic semiconductor (D) Insulator

Explanation 29:

• Correct Answer: (B)
• Reasoning: Group 13 elements (like Boron) are electron-deficient. When doped into Silicon (Group 14), they create “holes” (electron vacancies) which act as positive charge carriers, thus forming a p-type semiconductor.

Question 30: Which of the following is an example of an ionic solid? (A) Ice (B) Diamond (C) Potassium chloride (D) Copper

Explanation 30:

• Correct Answer: (C)
• Reasoning: Potassium chloride (KCl) is formed by electrostatic attraction between K+ cations and Cl- anions, making it an ionic solid. Ice is a hydrogen-bonded molecular solid, Diamond is a covalent network solid, and Copper is a metallic solid.

Question 31: What is the angle γ in a Hexagonal crystal system? (A) 90∘ (B) 120∘ (C) 60∘ (D) 109.5∘

Explanation 31:

• Correct Answer: (B)
• Reasoning: In a Hexagonal crystal system, a=b=c, α=β=90∘, and γ=120∘.

Question 32: In the density formula ρ=NA​×a3Z×M​, what does ‘M’ represent? (A) Mass of one atom (B) Molar mass of the element/compound (C) Atomic number (D) Mass of the unit cell

Explanation 32:

• Correct Answer: (B)
• Reasoning: ‘M’ represents the molar mass of the element or compound, typically in grams per mole (g/mol).

Question 33: Which of the following substances can be permanently magnetized? (A) Paramagnetic (B) Diamagnetic (C) Antiferromagnetic (D) Ferromagnetic

Explanation 33:

• Correct Answer: (D)
• Reasoning: Ferromagnetic substances (like Fe, Co, Ni) have domains that can be aligned by an external magnetic field and retain their alignment even after the field is removed, thus becoming permanently magnetized.

Question 34: Which of the following crystal structures has a 8:8 coordination number ratio? (A) Rock Salt (NaCl type) (B) Zinc Blende (ZnS type) (C) Fluorite (CaF$_2$ type) (D) Cesium Chloride (CsCl type)

Explanation 34:

• Correct Answer: (D)
• Reasoning: In the Cesium Chloride (CsCl) structure, both the cation (Cs+) and the anion (Cl−) have a coordination number of 8, leading to an 8:8 ratio. NaCl is 6:6, ZnS is 4:4, and CaF$_2$ is 8:4.

Question 35: A solid has a very high melting point and conducts electricity in the molten state but not in the solid state. What type of solid is it? (A) Molecular (B) Ionic (C) Metallic (D) Covalent

Explanation 35:

• Correct Answer: (B)
• Reasoning: Ionic solids fit this description. Their strong ionic bonds lead to high melting points. In the solid state, ions are fixed and cannot conduct electricity, but in the molten state or in solution, ions become mobile and conduct electricity.

Question 36: What is the general trend for conductivity in semiconductors with increasing temperature? (A) Decreases (B) Increases (C) Remains constant (D) First decreases, then increases

Explanation 36:

• Correct Answer: (B)
• Reasoning: In semiconductors, increasing temperature provides more thermal energy to electrons, allowing them to jump from the valence band to the conduction band, thus increasing the number of charge carriers (electrons and holes) and increasing conductivity.

Question 37: Which defect does not affect the density of the ionic crystal? (A) Schottky defect (B) Vacancy defect (C) Interstitial defect (D) Frenkel defect

Explanation 37:

• Correct Answer: (D)
• Reasoning: A Frenkel defect involves the displacement of an ion within the crystal, so no ions are lost from the crystal, and thus the density remains unchanged. Schottky defects and vacancy defects lead to a decrease in density, while interstitial defects lead to an increase in density.

Question 38: What is the unit of edge length ‘a’ required for density calculation if density is in g/cm3? (A) meters (m) (B) picometers (pm) (C) nanometers (nm) (D) centimeters (cm)

Explanation 38:

• Correct Answer: (D)
• Reasoning: To obtain density in g/cm3, the volume (a3) must be in cm3, which means the edge length ‘a’ must be in centimeters (cm). Conversions from pm or nm are often necessary.

Question 39: Which type of close packing arrangement is known as ABCABC… type? (A) Hexagonal Close Packing (HCP) (B) Cubic Close Packing (CCP) (C) Simple Cubic (SC) (D) Body-Centered Cubic (BCC)

Explanation 39:

• Correct Answer: (B)
• Reasoning: The ABCABC… layering sequence corresponds to Cubic Close Packing (CCP), which is identical to the Face-Centered Cubic (FCC) lattice. HCP uses an ABAB… layering sequence.

Question 40: If a solid is composed of atoms that are positive metal ions surrounded by a sea of delocalized electrons, it is a: (A) Molecular solid (B) Ionic solid (C) Metallic solid (D) Covalent solid

Explanation 40:

• Correct Answer: (C)
• Reasoning: This description perfectly matches the definition of a metallic solid, where positive metal ions (kernels) are held together by a mobile “sea” of electrons, responsible for their characteristic properties like conductivity and malleability.