CBSE Class 8 Science Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions MCQs Set 03

Download CBSE MCQs for Class 8 Science: Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions

Review structured MCQ sets for Class 8 Science Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions. Built according to official CBSE guidelines, these downloadable questions support daily revision and core concept reinforcement.

Chapter-wise Objective Questions: Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions

Navigate directly to the 50 objective questions for Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions using the digital viewer below. Each practice set includes verified answer keys, allowing students to instantly cross-check their work and identify areas requiring further revision.

Question: When salt and sugar dissolve in water to form a uniform mixture, what distinguishes this from the mixture created when chalk powder or sand is added to water?
A. The dissolved solute particles can be seen with magnification in both cases
B. The components remain evenly distributed throughout in the salt solution but separate into visible layers in chalk mixtures
C. Only the chalk mixture is considered a true mixture
D. Salt and sugar form solutions while chalk creates suspensions where particles remain visible
Show Answer & Explanation

Answer: (D) Salt and sugar form solutions while chalk creates suspensions where particles remain visible

Explanation:
The chapter explicitly defines solutions as uniform mixtures where solute dissolves evenly and is not separately visible. Chalk powder and sand, when mixed with water, form non-uniform mixtures where particles do not dissolve and can be observed either with the naked eye or magnification—these are not solutions.

Question: In Activity 9.1, when students progressively added salt to water and eventually found undissolved salt settling at the bottom, at what point did the solution transition from unsaturated to saturated?
A. When the first spoonful of salt completely dissolved
B. The moment undissolved salt appeared and could no longer dissolve completely
C. After five spoons of salt had been added
D. When the water temperature decreased
Show Answer & Explanation

Answer: (B) The moment undissolved salt appeared and could no longer dissolve completely

Explanation:
A saturated solution occurs when the solute stops dissolving and begins to settle, indicating the solvent has reached its maximum capacity at that temperature. The chapter states that once more solute cannot dissolve, the solution becomes saturated.

Question: Temperature affects the solubility of different substances in different ways. Based on Activity 9.2, which trend was observed for baking soda as water temperature increased from 20 °C to 70 °C?
A. Its solubility remained constant regardless of temperature change
B. It became less soluble, with more solid remaining undissolved
C. More of it dissolved at higher temperatures, demonstrating increased solubility
D. It began to crystallize out of solution
Show Answer & Explanation

Answer: (C) More of it dissolved at higher temperatures, demonstrating increased solubility

Explanation:
Activity 9.2 clearly showed that undissolved baking soda at 20 °C dissolved when temperature was raised to 50 °C, and dissolved even further at 70 °C. This directly demonstrates that solubility of solids in liquids increases with temperature increase.

Question: The chapter explains that oxygen dissolves in water to a small extent, yet this dissolved oxygen is crucial for aquatic life. Why does the solubility of oxygen in water decrease as water temperature increases, and what consequence does this have?
A. Oxygen molecules move faster at higher temperatures and escape from water more readily, reducing availability for fish and plants
B. Warmer water causes oxygen to form chemical bonds with water molecules, making it unavailable
C. The density of water increases at higher temperatures, trapping oxygen within
D. Oxygen becomes more concentrated in cooler water because it evaporates from warm water
Show Answer & Explanation

Answer: (A) Oxygen molecules move faster at higher temperatures and escape from water more readily, reducing availability for fish and plants

Explanation:
The chapter states that gas solubility generally decreases as temperature increases, and specifically notes that cold water can hold more dissolved oxygen, ensuring sufficient oxygen for aquatic life. When water warms, the dissolved oxygen decreases, potentially stressing aquatic organisms.

Question: A substance's density is defined as mass per unit volume. If an object has a mass of 16.4 g and occupies 5 cm³, and water has a density of 1 g/cm³, what can be predicted about this object's behaviour in water?
A. It will float because its density is less than water's density
B. It will sink because its density (3.28 g/cm³) exceeds water's density (1 g/cm³)
C. It will remain suspended between the top and bottom of water
D. Its behaviour cannot be determined without knowing the object's composition
Show Answer & Explanation

Answer: (B) It will sink because its density (3.28 g/cm³) exceeds water's density (1 g/cm³)

Explanation:
• Density = Mass ÷ Volume = 16.4 ÷ 5 = 3.28 g/cm³
• Water's density = 1 g/cm³
• Objects denser than water sink; those less dense float
• Since 3.28 > 1, the object will sink.

Question: Why are measuring cylinders deliberately designed with a narrow, tall shape rather than a wide, short shape like a beaker, according to the chapter?
A. Narrow cylinders are cheaper to manufacture than beakers
B. The narrow design allows for smaller divisions between markings and greater measurement accuracy
C. Narrow cylinders hold more liquid than beakers of the same height
D. The shape makes it easier to pour liquids without spillage
Show Answer & Explanation

Answer: (B) The narrow design allows for smaller divisions between markings and greater measurement accuracy

Explanation:
The chapter explains that narrower, taller measuring cylinders enable more precise measurement because the same volume change produces a greater height change, making smaller divisions possible and measurable. This design choice directly supports accuracy in volume determination.

Question: When reading the volume of a colourless liquid like water in a measuring cylinder, the chapter instructs to read at the bottom of the meniscus. Why is a different reading position required for coloured liquids?
A. Coloured liquids have different molecular structures that create inverted menisci
B. The colour prevents light from reaching the bottom of the liquid, making the bottom of the meniscus invisible
C. Coloured liquids form a curved surface with the colour concentrated at the top, making the top of the meniscus the appropriate reference point
D. There is no actual difference; the instruction applies equally to all liquids
Show Answer & Explanation

Answer: (C) Coloured liquids form a curved surface with the colour concentrated at the top, making the top of the meniscus the appropriate reference point

Explanation:
The chapter notes that for coloured liquids, the mark should coincide with the top of the meniscus because the colour makes the bottom of the curved surface difficult or impossible to read accurately. This is a practical adjustment for visibility and accuracy in measurement.

Question: According to the discussion of relative density in the chapter, if an aluminium block has a mass of 27 g and a volume of 10 cm³, what is its relative density with respect to water?
A. 0.27
B. 2.7
C. 27
D. 10
Show Answer & Explanation

Answer: (B) 2.7

Explanation:
Density of aluminium = 27 g ÷ 10 cm³ = 2.7 g/cm³. Relative density = Density of substance ÷ Density of water = 2.7 ÷ 1 = 2.7. This dimensionless number indicates aluminium is 2.7 times denser than water.

Question: The chapter presents the unusual property that ice floats on water. This occurs because water has its highest density at 4 °C, and when it freezes to ice at 0 °C, the particles arrange to occupy more space in a process called expansion. What is the significance of ice floating for aquatic ecosystems?
A. It allows ice to insulate the water underneath, maintaining temperatures warm enough for organisms to survive during winter
B. It causes the water beneath ice to become saltier, supporting more diverse marine life
C. It prevents water from freezing completely, which would otherwise eliminate all aquatic life
D. It increases the amount of dissolved oxygen available to fish and other organisms
Show Answer & Explanation

Answer: (A) It allows ice to insulate the water underneath, maintaining temperatures warm enough for organisms to survive during winter

Explanation:
The chapter explicitly states that because ice floats and forms a layer on top, it keeps the water underneath warm enough for fish and other creatures to survive even in extremely cold weather. This floating property acts as an insulating layer, protecting aquatic life from fatal freezing temperatures.

Question: When pressure is applied to different states of matter, its effect on density varies significantly. According to the chapter, which statement accurately describes how pressure affects gases versus solids?
A. Pressure decreases gas density but increases solid density equally
B. Pressure causes gas particles to move closer together and increase density, while solids are barely affected by pressure
C. Pressure has no effect on either gases or solids
D. Pressure increases the density of both equally because they have similar particle arrangements
Show Answer & Explanation

Answer: (B) Pressure causes gas particles to move closer together and increase density, while solids are barely affected by pressure

Explanation:
The chapter explains that for gases, increasing pressure causes particles to move closer together, decreasing volume and increasing density. For solids, particles are already very close together, so pressure causes negligible density changes. Liquids fall between these extremes with small effects.

Question: In the traditional salt production method of Ningel village, Manipur, salty water is collected and boiled in large metal pans until water evaporates and salt crystals form. What property of solutions does this evaporation process directly demonstrate?
A. That solutions are homogeneous mixtures where solute and solvent are inseparable
B. That solutes can be recovered from solutions by removing the solvent through heating or evaporation
C. That salt dissolves irreversibly and cannot be retrieved from solution
D. That only water, not salt, can be converted to a gas during heating
Show Answer & Explanation

Answer: (B) That solutes can be recovered from solutions by removing the solvent through heating or evaporation

Explanation:
The boiling and evaporation process shows that when the liquid solvent is removed by heat, the dissolved solid solute (salt) is left behind in crystalline form. This demonstrates that dissolution is reversible and the components of a solution can be separated through evaporation of the solvent.

Question: Asima Chatterjee used solvents and solutions extensively in her groundbreaking work developing anti-epileptic and anti-malarial drugs. What does her research approach suggest about the importance of understanding dissolution and solubility in pharmaceutical science?
A. Solvents are only useful for cleaning laboratory equipment in drug development
B. Understanding how to dissolve and extract compounds from plants is essential for isolating active medicinal ingredients that can be used in drug formulations
C. Solubility has no practical application beyond academic interest
D. All medicinal compounds are naturally soluble in water and require no special technique
Show Answer & Explanation

Answer: (B) Understanding how to dissolve and extract compounds from plants is essential for isolating active medicinal ingredients that can be used in drug formulations

Explanation:
The chapter's feature on Asima Chatterjee emphasizes that she used solvents and solutions to extract and isolate important compounds from medicinal plants. This illustrates that controlling solubility and understanding dissolution chemistry are fundamental skills for pharmaceutical research and drug development.

Question: When Reema flattened her 120 g piece of modeling clay from a compact cube (volume 60 cm³) into a thin sheet, what happened to the clay's density?
A. The density increased because the clay was spread out more
B. The density remained unchanged because neither the mass nor the fundamental composition of the clay changed
C. The density decreased because volume increased while mass stayed constant
D. The density would depend on the colour of the clay
Show Answer & Explanation

Answer: (C) The density decreased because volume increased while mass stayed constant

Explanation:
Density equals mass divided by volume. When the clay is flattened, its mass remains 120 g, but its volume increases. Since volume increases while mass stays constant, density (mass/volume) must decrease. The chapter emphasizes that density is independent of shape.

Question: In Activity 9.7, when an irregular stone is slowly lowered into a measuring cylinder containing 50 mL of water and the water level rises to 55 mL, what does the 5 mL rise in the water level actually represent?
A. The mass of the stone in grams
B. The volume of space the stone occupies, found by displacement
C. The density of the stone
D. The solubility of the stone in water
Show Answer & Explanation

Answer: (B) The volume of space the stone occupies, found by displacement

Explanation:
When an object displaces water in a measuring cylinder, the volume of displaced water equals the volume of the object. The rise from 50 mL to 55 mL means the stone displaced 5 mL of water, indicating the stone's volume is 5 cm³ (since 1 mL = 1 cm³).

Question: The chapter describes how hot air balloons work, explaining that hot air rises because it is less dense than cool air around it. What physical change causes hot air to become less dense than cool air?
A. Heating causes air particles to move away from each other and spread, increasing volume while mass remains constant, thus decreasing density
B. Hot air weighs less because the heat burns away some of the air molecules
C. Cool air becomes denser because it absorbs moisture from the environment
D. The colour of hot air changes, making it visually less dense
Show Answer & Explanation

Answer: (A) Heating causes air particles to move away from each other and spread, increasing volume while mass remains constant, thus decreasing density

Explanation:
The chapter explains that as temperature increases, particles of a substance move away and spread, increasing volume. Since Density = Mass/Volume and mass doesn't change during heating, the increase in volume causes density to decrease. This is why hot air rises—it's less dense than surrounding cool air.

Question: A cooking oil packet displays a volume of 1 litre but weighs only 910 grams, compared to water which would weigh 1000 grams for the same volume. What does this difference reveal about the relative densities?
A. Oil is denser than water because it weighs less
B. Water is denser than oil because the same volume of water weighs more
C. Oil and water have identical densities despite the weight difference
D. The difference in weight is due to the colour of the oil, not its density
Show Answer & Explanation

Answer: (B) Water is denser than oil because the same volume of water weighs more

Explanation:
Density is determined by comparing mass to volume. For the same volume (1 litre), oil has a mass of 910 g while water has approximately 1000 g. Since oil has less mass in the same volume, oil is less dense than water. This explains why oil floats on water.

Question: When an unpeeled orange floats in water but a peeled orange sinks, despite containing the same fruit inside, what principle from the chapter best explains this behaviour?
A. The peel contains air pockets that reduce the average density of the whole fruit below that of water, causing it to float
B. Peeled oranges are heavier due to the loss of protective material
C. Water dissolves the inside of peeled oranges, making them denser
D. The peel absorbs salt from the water, changing its density
Show Answer & Explanation

Answer: (A) The peel contains air pockets that reduce the average density of the whole fruit below that of water, causing it to float

Explanation:
An unpeeled orange floats because the peel contains air spaces that increase the overall volume without significantly increasing mass, resulting in an average density less than water's. When peeled, these air pockets are removed, and the denser fruit inside sinks. This demonstrates that density is a property of the entire object, not just the material itself.

Question: A student needs to measure 70 mL of water in a single step. According to the chapter's guidance, why would a 100 mL measuring cylinder be the best choice over a 50 mL or 250 mL cylinder?
A. A 100 mL cylinder is the most affordable option available
B. A 100 mL cylinder allows the measurement in one step like the 250 mL, but maintains better accuracy because its smallest division (1 mL) is smaller than that of the 250 mL cylinder (2 mL)
C. A 50 mL cylinder is actually better because it is smaller
D. All three cylinders would provide equally accurate results
Show Answer & Explanation

Answer: (B) A 100 mL cylinder allows the measurement in one step like the 250 mL, but maintains better accuracy because its smallest division (1 mL) is smaller than that of the 250 mL cylinder (2 mL)

Explanation:
• 50 mL cylinder: Cannot measure 70 mL in one step (too small)
• 100 mL cylinder: Can measure 70 mL in one step with smallest division of 1 mL
• 250 mL cylinder: Can measure 70 mL but has smallest division of 2 mL (less accurate)
• The 100 mL balances convenience and accuracy.

Question: According to the chapter, what is the relationship between the structure of Earth's layers (crust, mantle, outer core, inner core) and their respective densities?
A. All layers have equal density because they are composed of similar materials
B. Density decreases from the crust toward the center due to increasing temperature and pressure
C. Density increases progressively as one moves deeper toward Earth's center, with the crust being lightest and inner core being heaviest
D. Only the outer core has significant density; other layers are negligible
Show Answer & Explanation

Answer: (C) Density increases progressively as one moves deeper toward Earth's center, with the crust being lightest and inner core being heaviest

Explanation:
The chapter's 'Let us dig deeper' section explicitly states that Earth's outermost layer (the crust) is the lightest, and the density of different layers increases as one moves toward the centre. This occurs because pressure and temperature increase with depth, compacting materials and making them heavier and denser.

Question: When salt and sugar are mixed with water to create Oral Rehydration Solution, the resulting mixture tastes identical throughout each sip. Based on the chapter's explanation of solutions, what property of such mixtures accounts for this uniform taste?
A. The solute particles have settled at the bottom of the container
B. The solute particles are evenly distributed throughout the solvent
C. The solute particles are visible to the naked eye
D. The solute particles have chemically changed into new substances
Show Answer & Explanation

Answer: (B) The solute particles are evenly distributed throughout the solvent

Explanation:
The chapter explicitly states that when salt and sugar are added to water, they form a mixture in which the components are evenly distributed throughout. This uniform distribution is what makes a solution a uniform mixture, ensuring each sip tastes the same regardless of how much you drink.

Question: In Activity 9.2, when baking soda was heated from 20 °C to 50 °C to 70 °C, progressively more of the solid baking soda dissolved at each temperature increase. What does this sequence of observations demonstrate about the relationship between temperature and solubility?
A. Solubility of solids in water is unaffected by temperature changes
B. Solubility of solids in water generally increases as temperature increases
C. Solubility of all substances decreases uniformly with heating
D. Temperature only affects gas solubility, not solid solubility
Show Answer & Explanation

Answer: (B) Solubility of solids in water generally increases as temperature increases

Explanation:
The chapter reports that water at 70 °C dissolved more baking soda than water at 50 °C, which in turn dissolved more than water at 20 °C. This directly demonstrates that for most substances, solubility increases with temperature. The chapter explicitly states: 'For most of the substances, the solubility increases with an increase in temperature.'

Question: A measuring cylinder marked 100 mL shows 10 divisions between the 10 mL and 20 mL marks. What is the smallest volume this cylinder can accurately measure?
A. 0.1 mL
B. 0.5 mL
C. 1 mL
D. 5 mL
Show Answer & Explanation

Answer: (C) 1 mL

Explanation:
• 10 mL volume difference between marks
• 10 divisions between these marks
• 10 ÷ 10 = 1 mL per small division
The chapter confirms this calculation in Activity 9.4 and states that 100 mL cylinders typically have a smallest readable value of 1 mL.

Question: According to the chapter, why does an unpeeled orange float on water while a peeled orange sinks, even though both contain the same fruit?
A. The peel adds extra mass to the orange
B. The peel has a lower density and creates air pockets, making the whole orange less dense than water
C. Peeling removes salt from the orange's surface
D. The fruit itself becomes denser when exposed to air
Show Answer & Explanation

Answer: (B) The peel has a lower density and creates air pockets, making the whole orange less dense than water

Explanation:
The unpeeled orange floats because the peel is less dense and contains air pockets, making the overall density of the unpeeled orange less than water. When peeled, these air pockets are removed, increasing the overall density above that of water, causing it to sink. This demonstrates that density—not just the substance itself—determines whether an object floats or sinks.

Question: A stone with a mass of 16.4 g occupies a volume of 5 cm³. Given that water has a density of 1 g/cm³, what will happen to this stone in water?
A. It will float because the stone has less mass than water
B. It will float because its density is less than water's density
C. It will sink because its density is greater than water's density
D. Its behaviour cannot be determined without knowing the shape
Show Answer & Explanation

Answer: (C) It will sink because its density is greater than water's density

Explanation:
Calculating density: 16.4 g ÷ 5 cm³ = 3.28 g/cm³. Since 3.28 g/cm³ is much greater than water's density of 1 g/cm³, the stone is much denser than water and will sink. The chapter explains that objects with density greater than the surrounding liquid will sink.

Question: In the traditional salt production method of Ningel village, Manipur, salty water is boiled in large metal pans until water evaporates and salt crystals form. What fundamental property of solutions does this process directly illustrate?
A. Solutes can be separated from solvents through evaporation
B. All solutions are permanent and cannot be broken down
C. Heating always increases the solubility of all substances
D. Salt becomes insoluble when water is heated
Show Answer & Explanation

Answer: (A) Solutes can be separated from solvents through evaporation

Explanation:
By boiling the salt solution, the water (solvent) evaporates completely, leaving behind the dissolved salt (solute) in the form of crystals. This demonstrates that even though a solute dissolves in a solvent to form a uniform mixture, the two components can be separated through physical means like evaporation. The chapter discusses solutions as uniform mixtures where components remain mixed unless separated by such processes.

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