Previous Year MCQs on Silicon Dioxide (SiO2)
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Which of the following is correct about silicon dioxide?
- It is a giant covalent network solid with tetrahedral coordination.
- It has a simple molecular structure like CO₂.
- It is a good conductor of electricity in solid state.
- It has low melting point due to weak van der Waals forces.
Answer
Correct Answer: A
SiO₂ has a three-dimensional giant covalent network structure in which each Si is tetrahedrally bonded to four oxygen atoms and each oxygen is bonded to two silicon atoms. Unlike CO₂ (simple molecule), SiO₂ does not form π-bonds easily due to large size of Si, hence it does not form O=Si=O. It is an insulator with very high melting point (~1710 °C). Options B, C, D are characteristics of CO₂, not SiO₂.
Quartz is an example of
- Chain silicate
- Sheet silicate
- Three-dimensional network silicate
- Cyclic silicate
Answer
Correct: C Quartz is a tectosilicate (three-dimensional network silicate) in which every oxygen is shared between two tetrahedra, giving the empirical formula SiO₂. Chain = pyroxenes, sheet = micas, cyclic = beryl.
Which of the following statements is INCORRECT about crystalline and amorphous silica?
- Amorphous silica has a sharp melting point while crystalline silica does not.
- Fused silica has extremely low coefficient of thermal expansion.
- Crystalline silica is responsible for silicosis.
- Both have the same local tetrahedral SiO₄ unit.
Answer
Incorrect statement: A
Amorphous silica (fused silica) softens over a range and does not have a sharp melting point, whereas crystalline forms transform or melt at definite temperatures. The other three statements are correct.
The disease caused by inhalation of fine particles of crystalline silica dust is known as
- Byssinosis
- Silicosis
- Asbestosis
- Bagassosis
Answer
B – Silicosis Classic occupational lung disease due to respirable crystalline silica (quartz, cristobalite, tridymite). Byssinosis = cotton dust, Asbestosis = asbestos, Bagassosis = sugarcane dust.
Which form of silica is mainly responsible for silicosis?
- Amorphous silica
- Crystalline silica
- Colloidal silica
- Fumed silica
Answer
B – Crystalline silica Only the crystalline polymorphs (quartz, cristobalite, tridymite) are highly fibrogenic and cause classic silicosis. Amorphous silica is relatively harmless.
In the structure of SiO₂
- Each Si is sp² hybridised and O is sp³ hybridised
- Si is sp³ hybridised and O is sp² hybridised
- Both Si and O are sp³ hybridised
- Si is sp³ hybridised and O is sp hybridised with a lone pair in p-orbital
Answer
C Silicon in SiO₂ is sp³ hybridised (tetrahedral geometry). Oxygen is also considered sp³ hybridised with two lone pairs and two σ-bonds to silicon atoms. The bond angle at oxygen is ~140–150° in the network, close to tetrahedral.
The structure of SiO₂ is best described as:
- Simple molecular
- Layered
- Giant covalent network
- Ionic
Answer
Quartz is a:
- Chain silicate
- Sheet silicate
- Cyclic silicate
- Framework (3D) silicate
Answer
In SiO₂, the coordination number of silicon and oxygen respectively are:
- 4 and 2
- 4 and 4
- 6 and 3
- 2 and 4
Answer
SiO₂ is a solid at room temperature while CO₂ is a gas because:
- SiO₂ has higher molecular mass
- Si cannot form pπ–pπ multiple bonds easily
- Si–O bond is weaker than C–O bond
- CO₂ is non-polar
Answer
Which form of silica has no sharp melting point?
- α-Quartz
- Cristobalite
- Fused silica (amorphous)
- Tridymite
Answer
The hybridization of silicon in SiO₂ is:
- sp
- sp²
- sp³
- sp³d
Answer
Which property of SiO₂ is responsible for its use in optical fibres?
- High refractive index
- Low thermal expansion & high transparency
- High electrical conductivity
- Magnetic nature
Answer
The reason for very high melting point of SiO₂ is:
- Strong Si–O covalent bonds in 3D network
- Van der Waals forces
- Hydrogen bonding
- Ionic bonding
Answer
In the structure of SiO₄ tetrahedra in quartz, each oxygen atom is shared by:
- One tetrahedron
- Two tetrahedra
- Three tetrahedra
- Four tetrahedra
Answer
Fused silica is used for making telescope mirrors because it has:
- Zero coefficient of thermal expansion
- Very low coefficient of thermal expansion
- High density
- High refractive index
Answer
SiO₂ is an acidic flux because:
- It reacts with basic impurities like CaO, MgO
- It is basic in nature
- It is neutral
- It reacts with acids
Answer
Amorphous form of SiO₂ is:
- Quartz
- Cristobalite
- Fused silica
- Tridymite
Answer
The Si–O–Si bond angle in SiO₂ network is approximately:
- 109.5°
- 120°
- 144°–150°
- 180°
Answer
Which of the following has a 3D network structure?
- CO₂
- SiO₂
- SO₂
- Both (A) and (B)
Answer
Glass is basically:
- Crystalline SiO₂
- Supercooled liquid of silicate
- Polymer
- Metallic solid
Answer
Piezoelectric material used in watches and oscillators is:
- α-Quartz
- Fused silica
- Sodium silicate
- Silicon carbide
Answer
Read also: Silica: Preparation, Properties, Bonding, Structure, Comparison and Uses