All questions of Materials Around Us for Class 6 Exam

Mass is the quantity of matter in an object, measured in grams (g) or kilograms (kg).

Mass is the measure of the amount of matter in an object, typically measured in grams or kilograms.

Gas fills the space of its container and has mass, unlike solids and liquids which have a definite shape or volume.

Wood is opaque, meaning it does not allow light to pass through.

Transparency refers to how clearly one can see through a material.

Understanding Why Oil Floats on Water
When we observe oil floating on water, it's important to understand the scientific principles behind this phenomenon. The key concept here is density.
Density Explained
- Density is defined as mass per unit volume. It helps us understand how heavy a substance is for a given size.
- Different substances have different densities, which affects how they behave when mixed.
Comparison of Oil and Water Density
- Water has a density of approximately 1 gram per cubic centimeter (g/cm³).
- Most oils, such as vegetable oil or motor oil, have a density less than 1 g/cm³, typically around 0.8 to 0.9 g/cm³.
Why Oil Floats
- Since oil is less dense than water, it cannot sink; instead, it floats on top.
- This is similar to how a lighter object, like a rubber ball, floats on water while a denser object, like a rock, sinks.
Implications of Oil Floating
- The floating behavior of oil can lead to environmental issues, such as oil spills, where oil forms a layer on top of water bodies, affecting marine life.
- Understanding this concept is crucial in science and environmental studies.
In summary, oil floats on water primarily because it is less dense than water. This fundamental principle of density helps us comprehend various natural phenomena and their implications.

Understanding Solubility
When a soluble material is mixed with water, it undergoes a process called dissolution. Let's explore this phenomenon in detail:
What is Solubility?
- Solubility refers to the ability of a substance to dissolve in a solvent, in this case, water.
- A soluble material is one that can completely mix with water to form a solution.
The Process of Dissolving
- When a soluble material (like sugar or salt) is added to water, the individual particles of the material are pulled apart by the water molecules.
- These water molecules surround the particles, effectively breaking them down into smaller units.
Why It Dissolves Completely?
- The interaction between water molecules and the particles of the soluble material is strong enough to overcome the forces holding the particles together.
- As a result, the material spreads evenly throughout the water, leading to a homogeneous mixture known as a solution.
Key Points to Remember
- Complete Dissolution: The soluble material dissolves fully, meaning it cannot be seen in its original form.
- No Layer Formation: Unlike insoluble materials that may sink or float, soluble materials integrate into the water.
In conclusion, when a soluble material is mixed with water, it dissolves completely (option B), creating a uniform solution that is a hallmark of solubility. This process is essential in various applications, from cooking to chemical reactions.

Sugar dissolves in water, forming a solution, while sand, chalk, and clay do not dissolve in water.

Understanding Insoluble Materials
Insoluble materials are substances that do not dissolve in water. Among the options provided, sand is the only material that is considered insoluble.
Why is Sand Insoluble in Water?
- Particle Size: Sand consists of larger particles compared to sugar and salt. These larger particles do not interact effectively with water molecules.
- Lack of Chemical Interaction: Sand is primarily composed of silicon dioxide (SiO2). It does not form bonds with water molecules, which is necessary for dissolution.
Comparison with Other Options
- Sugar:
- Solubility: Sugar dissolves readily in water due to its molecular structure, which allows it to interact with water molecules effectively.
- Salt:
- Solubility: Similar to sugar, salt (sodium chloride) dissolves in water as the ionic bonds in salt break apart in the presence of water, allowing it to disperse.
- Lemon Juice:
- Solubility: Lemon juice is a liquid solution containing various acids and sugars, which are soluble in water.
Conclusion
In summary, among the given options, sand is the only substance that does not dissolve in water, making it the correct answer. Understanding the properties of materials based on their interaction with water is crucial in science, especially in chemistry and environmental studies.

Understanding Material Selection
When creating objects, the choice of material is crucial because different materials possess unique properties that make them suitable for specific functions. Here’s a detailed explanation of why this is important.
Specific Properties of Materials
- Strength: Some materials, like metals, are strong and can withstand heavy loads. This makes them ideal for construction and machinery.
- Weight: Lightweight materials, such as plastics and aluminum, are preferred for items like airplanes and packaging to improve efficiency and reduce energy consumption.
- Durability: Certain materials resist wear and tear better than others. For example, rubber is used for tires because it can withstand friction and impacts.
- Conductivity: Materials like copper are excellent conductors of electricity, making them essential for wiring and electrical components.
- Insulation: Materials such as foam or fiberglass are used for insulation because they can trap air and reduce heat transfer.
Suitability for Different Purposes
- Functionality: The intended use of an object dictates the choice of material. For instance, kitchen utensils need to be heat-resistant and easy to clean, leading to the use of stainless steel or silicone.
- Aesthetic Appeal: While functionality is key, the appearance of materials also matters. Wood, glass, and ceramics can provide beauty and elegance to furniture and decor.
- Cost and Availability: Economic factors also influence material selection. Common and affordable materials are often chosen to keep costs down while meeting quality standards.
In conclusion, each material's specific properties make it suitable for different uses, ensuring that objects perform effectively and meet the required standards. This careful selection process reflects the diverse needs of society and enhances the functionality of everyday items.

Material Used for Making Windows: Glass
Glass is commonly used for making windows because of its transparency and durability. Let's explore why glass is the preferred material for windows:

Transparency:
- Glass is transparent, allowing natural light to enter a space and providing a clear view of the outside.
- This transparency creates a sense of openness and connection to the surroundings.

Durability:
- Glass is a durable material that can withstand various weather conditions, including rain, wind, and sunlight.
- It is also resistant to scratches and does not deteriorate easily over time.

Insulation:
- Glass windows can be designed to provide thermal insulation, helping to maintain a comfortable indoor temperature.
- Double or triple-pane glass windows with gas fills can enhance energy efficiency by reducing heat loss.

Aesthetics:
- Glass windows come in various styles, sizes, and designs, allowing for customization to complement the architectural style of a building.
- They can enhance the visual appeal of a space and create a modern and sleek look.

Ease of Maintenance:
- Glass windows are relatively easy to clean and maintain compared to other materials like wood or metal.
- Regular cleaning with a glass cleaner can keep windows looking clear and sparkling.
In conclusion, the transparency, durability, insulation properties, aesthetics, and ease of maintenance make glass the ideal material for making windows in buildings. Its versatility and functionality have made it a popular choice among architects, builders, and homeowners.

Hard materials resist compression and scratches, whereas soft materials are easily compressed.

Understanding Classification
Classification is the process of grouping objects based on shared characteristics or properties. This method helps in organizing and simplifying the vast array of items that we encounter in our daily lives.
Key Aspects of Classification:
- Definition: Classification involves sorting items into categories that share similarities, making them easier to study and understand.
- Purpose: The main goal is to create order among diverse objects, which helps in identifying, studying, and utilizing them effectively.
- Examples: Common examples of classification include:
- Living Organisms: In biology, organisms are classified into kingdoms, phyla, and species based on traits like structure and genetics.
- Library Systems: Books are classified by genre, author, or subject matter to facilitate easier access and organization.
- Household Items: Items in a kitchen can be classified as utensils, cookware, or appliances based on their function.
Benefits of Classification:
- Enhanced Understanding: By categorizing items, we can better understand their relationships and differences.
- Efficiency: Classification allows for quicker identification and retrieval of information, whether in studying or practical applications.
- Facilitates Communication: When items are classified, it becomes easier to discuss and share information about them using common terms.
In summary, classification is a vital process in organizing knowledge and objects, making it an essential concept in various fields of study and everyday life.

Standard Unit of Mass in SI
The International System of Units (SI) is a globally recognized system used for measuring various physical quantities, including mass.
What is the Standard Unit of Mass?
- The standard unit of mass in the SI system is the kilogram (kg).
Reasons Why Kilogram is the Standard Unit:
- Definition:
- A kilogram is defined as the mass of a specific prototype kept at the International Bureau of Weights and Measures (BIPM) in France.
- Uniformity:
- The kilogram provides a consistent measurement across different scientific and practical applications, ensuring that everyone measures mass using the same standard.
- Usage:
- In scientific experiments, industry, and everyday life, the kilogram is widely adopted for measuring mass, making it a universal standard.
Other Units of Mass:
- Gram:
- While the gram (g) is also a unit of mass, it is a smaller unit. One kilogram equals 1,000 grams.
- Pound:
- The pound (lb) is commonly used in the United States and some other countries but is not part of the SI system.
- Litre:
- A litre (L) is a unit of volume, not mass, and is therefore not related to this question.
Conclusion
In summary, the correct answer is option 'B', the kilogram, as it is the standard unit of mass in the SI system, ensuring uniformity and consistency in measurement across the globe.

Understanding Lustrous Materials
Lustrous materials are those that have a shiny appearance and reflect light effectively. They are often metals or materials with a smooth surface. Let’s take a closer look at the options provided:
Options Explained
- Wood: Wood is a natural material that does not have a shiny surface. It typically has a matte finish and absorbs light rather than reflecting it.
- Iron: Iron is a metal known for its lustrous characteristics. When polished, it exhibits a shiny surface that reflects light, making it a classic example of a lustrous material.
- Rubber: Rubber is a synthetic material that usually has a dull appearance. It does not reflect light well and is not considered lustrous.
- Paper: Paper is another non-lustrous material. It tends to have a flat finish, absorbing light rather than reflecting it.
Conclusion
Among the options provided, iron stands out as the only lustrous material. Its metallic qualities enable it to shine when polished, making it a common choice for various applications where aesthetics and light reflection are important.
In summary, the correct answer is option 'B' (Iron) because it possesses the shiny, reflective properties characteristic of lustrous materials.

Understanding Transparent Materials
When it comes to light transmission, materials can be categorized into three main types: opaque, transparent, and translucent. Each type interacts with light differently.
Types of Materials
- Opaque: These materials do not allow any light to pass through. Examples include wood, metal, and thick fabrics. When light hits an opaque object, it is either absorbed or reflected, preventing visibility through the material.
- Transparent: Transparent materials allow light to pass through them clearly. This means that objects on the other side can be seen distinctly. Common examples include clear glass and clean water. The clarity of transparent materials makes them ideal for applications like windows and lenses.
- Translucent: Translucent materials allow some light to pass through, but not enough to see objects clearly. Examples include frosted glass and certain types of plastic. While light can filter through, the details on the other side remain blurred.
Key Characteristics of Transparent Materials
- Clarity: Transparent materials provide a clear view of objects behind them, making them essential for visibility.
- Light Transmission: They enable maximum light transmission, which is crucial for applications requiring illumination and visibility.
- Versatility: Used in various settings, from household windows to high-tech optical devices, transparent materials are vital in modern life.
In conclusion, the correct answer to the question is option 'B' – transparent materials are the ones that allow light to pass through them clearly, making them distinct from opaque and translucent materials.

Glass is transparent, allowing light to pass through, making it ideal for windows.

Understanding Soft Materials
Soft materials are characterized by their lower hardness, flexibility, and ability to deform easily under pressure. Let's explore why cotton is considered a soft material compared to the other options.
Comparison of Materials
- Iron:
- Iron is a hard, strong metal known for its durability and resistance to deformation. It is commonly used in construction and manufacturing, making it one of the hardest materials listed.
- Wood:
- While wood is softer than iron, it can still be relatively hard depending on the type of wood. Woods like oak or maple can be quite dense and are used for furniture, which gives them a moderate hardness.
- Cotton:
- Cotton is a natural fiber derived from cotton plants. It is soft, flexible, and comfortable to touch. Cotton fibers can bend and compress easily, making them ideal for clothing and bedding. It lacks the rigidity of metals and the density of some woods, firmly categorizing it as a soft material.
- Glass:
- Glass is a hard, brittle material that can shatter under stress. Although it can be molded when heated, once it cools, it becomes quite hard.
Conclusion
Among the options provided, cotton stands out as the softest material. Its unique properties, including softness and flexibility, make it suitable for various everyday applications, distinguishing it from the harder materials like iron, wood, and glass.

Ancient Indian pottery was primarily made of clay, which was shaped and baked in kilns to create durable terracotta pots.

Paper is derived from trees, which are a natural resource, while plastic, glass, and metal are man-made materials.