Carbon and its Compounds Quiz - ICSE Class 8 Science
Free practice quiz: Carbon and its Compounds (ICSE Class 8 Science). 49 multiple-choice questions with answers and explanations. Play online, no sign-up needed.
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The process of converting coal into coke, coal gas, and coal tar is known as:
- Combustion
- Distillation
- Cracking
- Pyrolysis
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Answer: D. Pyrolysis
Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. This is precisely what happens when coal is heated strongly in the absence of air to produce coke, coal gas, and coal tar.
Carbon monoxide (CO) is a toxic gas because it:
- Reacts vigorously with oxygen
- Forms carbonic acid in the lungs
- Combines with hemoglobin in the blood, reducing oxygen transport
- Dissolves readily in water to form a weak acid
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Answer: C. Combines with hemoglobin in the blood, reducing oxygen transport
Carbon monoxide binds to hemoglobin in red blood cells with a much higher affinity than oxygen. This forms carboxyhemoglobin, which reduces the blood's capacity to carry oxygen to the body's tissues, leading to oxygen deprivation and toxicity.
Which substance is used to remove color from colored solutions by adsorption?
- Sodium chloride
- Activated charcoal
- Sulfuric acid
- Water
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Answer: B. Activated charcoal
Activated charcoal has a highly porous structure with a large surface area. This large surface area allows it to adsorb impurities, including colored substances, from solutions. This process is used in decolorization.
Which allotrope of carbon has a structure described as 'sheets' of carbon atoms arranged in hexagonal rings, with weak forces between the sheets?
- Diamond
- Fullerene
- Amorphous carbon
- Graphite
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Answer: D. Graphite
Graphite's structure consists of planar layers of carbon atoms, where each carbon is bonded to three others in hexagonal rings. These layers are held together by weak van der Waals forces, allowing them to slide over each other.
Which statement about carbon dioxide is incorrect?
- It is a greenhouse gas.
- It is essential for photosynthesis.
- It is produced by respiration.
- It is less dense than air.
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Answer: D. It is less dense than air.
Carbon dioxide (CO2) has a molar mass of approximately 44 g/mol. The average molar mass of dry air is about 29 g/mol. Therefore, carbon dioxide is denser than air and will settle at the bottom of a container. The other statements are correct.