CBSE Class 8 Science Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions MCQs Set 02

Science Objective Questions and Answers: Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions

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Access the complete set of multiple-choice questions for Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official CBSE textbooks.

Question: When chalk powder is mixed with water, what distinguishes this mixture from the mixture of salt dissolved in water?
A. Chalk powder forms a uniform mixture that appears as a single phase
B. Chalk particles remain visibly separate and do not dissolve evenly throughout the water
C. Chalk powder becomes a solution because its components are uniformly distributed
D. Chalk and water create a saturated solution at room temperature
Show Answer & Explanation

Answer: (B) Chalk particles remain visibly separate and do not dissolve evenly throughout the water

Explanation:
The chapter describes how chalk powder in water creates a non-uniform mixture where components are not evenly distributed, contrasting sharply with salt or sugar dissolving to form uniform solutions. The particles settle or remain visible rather than disappearing into the liquid.

Question: According to the discussion in Activity 9.1, what can be inferred about water's capacity to dissolve salt once undissolved salt appears at the bottom of the container?
A. The water can dissolve more salt if stirred more vigorously
B. The water has reached its maximum dissolving capacity at that temperature
C. Adding more water would not help dissolve the remaining salt
D. The salt has become a non-uniform mixture that cannot be separated
Show Answer & Explanation

Answer: (B) The water has reached its maximum dissolving capacity at that temperature

Explanation:
When undissolved salt settles at the bottom despite continued stirring, it signals that the water has reached saturation—the solvent can no longer dissolve additional solute at that specific temperature. This is the defining characteristic of a saturated solution.

Question: Why is the solubility of oxygen in water considered critical for aquatic ecosystems, despite oxygen being present only in minute quantities?
A. Oxygen becomes a saturated solution in all water bodies
B. Even small dissolved amounts of oxygen are sufficient to sustain all aquatic plant and animal life
C. Minute quantities prevent water from forming non-uniform mixtures
D. Oxygen dissolves faster in cold water than in salt water
Show Answer & Explanation

Answer: (B) Even small dissolved amounts of oxygen are sufficient to sustain all aquatic plant and animal life

Explanation:
The chapter states that dissolved oxygen, though present in minute quantities, is what sustains all aquatic life including plants, fishes, and organisms. The key is not the quantity but the essential role this dissolved gas plays in supporting life in water.

Question: How does the design of a measuring cylinder as narrow and tall rather than wide and short relate to measurement accuracy?
A. A narrow cylinder allows water to form a more pronounced meniscus for easier reading
B. Narrow design reduces the smallest measurable volume increment per division
C. Tall shape prevents gases from escaping during measurement
D. Wide cylinders absorb more heat and affect liquid density
Show Answer & Explanation

Answer: (B) Narrow design reduces the smallest measurable volume increment per division

Explanation:
• Narrow cylinders allow smaller height changes per unit volume
• More divisions fit in the same height, creating smaller increments
• This enables more precise measurement of small volumes compared to wide, short designs

Question: Based on the information about density and the layers of Earth, what relationship exists between an object's position within Earth's layers and its density?
A. Density remains constant throughout all layers of Earth
B. Density generally increases as one moves deeper toward Earth's center
C. The crust is the densest layer because it is exposed to atmosphere
D. Density in the outer core is lower than in the crust due to temperature effects
Show Answer & Explanation

Answer: (B) Density generally increases as one moves deeper toward Earth's center

Explanation:
The chapter explicitly states that Earth's crust is the lightest layer and that the density of different layers increases as one moves toward the centre, driven by increased pressure and temperature at greater depths.

Question: In the context of Asima Chatterjee's work on medicinal plants, what was the primary purpose of using solvents and solutions in her research?
A. To increase the temperature of plant materials for faster extraction
B. To extract and isolate important compounds from medicinal plants
C. To create saturated solutions that preserve plant effectiveness
D. To dissolve plant materials so they could be used as medicines directly
Show Answer & Explanation

Answer: (B) To extract and isolate important compounds from medicinal plants

Explanation:
The chapter notes that Asima Chatterjee used solvents and solutions extensively to extract and isolate important compounds from medicinal plants as part of her work on anti-epileptic and anti-malarial drugs.

Question: What does the traditional salt production method in Ningel village, Manipur demonstrate about the practical application of solution chemistry?
A. That salt cakes must be saturated solutions to have medicinal value
B. That evaporation is used to separate salt (solute) from salt solution (solvent) through crystallization
C. That salt wells produce only unsaturated solutions
D. That traditional methods cannot achieve the same results as modern chemistry
Show Answer & Explanation

Answer: (B) That evaporation is used to separate salt (solute) from salt solution (solvent) through crystallization

Explanation:
The heritage section describes how salty water is collected and boiled in pans, allowing water to evaporate and salt crystals to form. This illustrates the practical reversal of dissolution—separating solute from solvent through heating and evaporation.

Question: Why would a 50 mL measuring cylinder be less suitable than a 100 mL cylinder for measuring 70 mL of water in a single step?
A. The 50 mL cylinder cannot measure volumes above 50 mL in any circumstances
B. A 50 mL cylinder has a smaller total capacity, requiring the measurement to be done in two steps
C. The smaller cylinder produces less accurate readings due to larger individual division values
D. The meniscus in a 50 mL cylinder curves differently than in larger cylinders
Show Answer & Explanation

Answer: (B) A 50 mL cylinder has a smaller total capacity, requiring the measurement to be done in two steps

Explanation:
Since a 50 mL cylinder can only hold up to 50 mL, measuring 70 mL requires at least two steps: first measuring 50 mL, then adding another 20 mL. A 100 mL cylinder allows the entire 70 mL to be measured in a single step, improving convenience.

Question: What physical process explains why hot air balloons rise into the atmosphere according to principles discussed in the chapter?
A. Hot air has greater mass than cool air surrounding it
B. Heated air expands, decreasing its density so it becomes lighter than cooler air below
C. The balloon material absorbs heat and becomes less dense
D. Cool air is pushed downward by the balloon's weight
Show Answer & Explanation

Answer: (B) Heated air expands, decreasing its density so it becomes lighter than cooler air below

Explanation:
The chapter explains that as temperature increases, particles move away and spread, increasing volume while mass stays constant. Since density equals mass divided by volume, lower density means the hot air rises relative to denser cool air—the exact principle behind hot air balloons.

Question: How do the properties of water allow it to dissolve both salt and sugar while oil does not dissolve these substances?
A. Oil molecules move faster than water molecules at room temperature
B. Water's molecular structure creates conditions for uniform mixing with polar solutes like salt and sugar
C. Salt and sugar are liquids that can only mix with liquid solvents, not oils
D. Oil becomes a saturated solution when salt or sugar is added to it
Show Answer & Explanation

Answer: (B) Water's molecular structure creates conditions for uniform mixing with polar solutes like salt and sugar

Explanation:
While the chapter raises the question of why water dissolves salt and sugar but oil does not, it establishes water as a good solvent for these substances. This reflects fundamental molecular differences—water's ability to dissolve polar substances effectively makes it superior to non-polar oils for these particular solutes.

Question: In Activity 9.5, why must the eyes be positioned at the level of the bottom of the meniscus rather than above or below it when reading the volume in a measuring cylinder?
A. The meniscus shape changes if viewed from different angles, affecting the reading's accuracy
B. Viewing from eye level ensures the most accurate reading where the curved surface is lowest
C. The water evaporates faster if observed from above the cylinder
D. Liquid density increases when viewed from certain angles
Show Answer & Explanation

Answer: (B) Viewing from eye level ensures the most accurate reading where the curved surface is lowest

Explanation:
Meniscus curvature means the water level appears different depending on viewing angle. Reading at eye level, aligned with the bottom of the curve, provides the standard, most accurate measurement point for water and other colourless liquids.

Question: What inference can be made about why different sizes of measuring cylinders exist (5 mL, 10 mL, 25 mL, 50 mL, 100 mL, 250 mL) rather than just having one large universal cylinder?
A. Smaller cylinders have higher solubility and larger ones have lower solubility
B. Different cylinder sizes provide different levels of accuracy depending on the volume being measured
C. Larger cylinders can only measure gases while smaller ones measure liquids
D. All cylinders measure with equal precision regardless of size
Show Answer & Explanation

Answer: (B) Different cylinder sizes provide different levels of accuracy depending on the volume being measured

Explanation:
• Smaller cylinders have finer divisions and lower smallest measurable volumes
• Larger cylinders can measure bigger volumes but with less precision
• Selecting the appropriate size matches measurement needs to accuracy requirements—measuring 5 mL in a 500 mL cylinder would be imprecise

Question: Based on the discussion of relative density in the chapter, why is an aluminium block with relative density 2.7 denser than an ice block floating in water?
A. Aluminium is a solid while ice is frozen water in a different state
B. Aluminium's mass per unit volume (2.7 times water's density) is greater than ice's density
C. Relative density only applies to metals and not to frozen water
D. Ice contains dissolved oxygen which reduces its density
Show Answer & Explanation

Answer: (B) Aluminium's mass per unit volume (2.7 times water's density) is greater than ice's density

Explanation:
Relative density compares a substance's density to water's density. An aluminium block at 2.7 g/cm³ is 2.7 times denser than water, while ice (which floats) must be less dense than water. Therefore, aluminium is definitely denser than ice.

Question: How does the special property of water—having its highest density at 4 °C rather than at 0 °C—relate to the survival of aquatic organisms in cold climates?
A. Water at 4 °C is warmer so organisms prefer that temperature
B. Because ice forms a floating layer on top of liquid water below, insulating and protecting aquatic life from freezing
C. Organisms can only survive at exactly 4 °C and will die at other temperatures
D. Water density prevents any ice formation regardless of temperature
Show Answer & Explanation

Answer: (B) Because ice forms a floating layer on top of liquid water below, insulating and protecting aquatic life from freezing

Explanation:
The chapter explains that water's unusual property causes ice to be less dense, so it floats rather than sinks. This floating ice layer acts as an insulating barrier, allowing liquid water underneath to remain warm enough for fish and other creatures to survive even in extremely cold weather.

Question: Why would adding salt to fresh water make it possible for an egg to float, whereas the egg sinks in ordinary tap water alone?
A. Salt dissolves completely, creating a uniform solution that is less dense
B. Adding salt increases the solution's density, eventually making it denser than the egg
C. The egg's mass decreases when submerged in salt water
D. Salt changes the egg's shape, reducing its volume
Show Answer & Explanation

Answer: (B) Adding salt increases the solution's density, eventually making it denser than the egg

Explanation:
The chapter discusses density's role in floating and sinking. When salt dissolves in water, it increases the solution's overall density. If the salt solution becomes denser than the egg, the egg will float—similar to how objects float in the Dead Sea, a much higher-density solution than freshwater.

Question: When sugar and salt are added to water in Oral Rehydration Solution, the mixture tastes uniform throughout because the solute components are distributed in a particular way. What is this property of the mixture called?
A. a non-uniform mixture
B. a uniform mixture or solution
C. a saturated solution
D. an unsaturated solution
Show Answer & Explanation

Answer: (B) a uniform mixture or solution

Explanation:
The chapter explicitly states that when sugar and salt are added to water, they form a mixture in which the components are evenly distributed throughout. This describes a uniform mixture, which is defined as a solution in the context of the chapter.

Question: In Activity 9.2, when baking soda at 50 °C dissolved further after more baking soda was added, and then dissolved even more at 70 °C, what scientific principle does this sequence of observations best illustrate?
A. pressure increases the solubility of solids
B. temperature is independent of solubility changes
C. the solubility of most solids increases with rising temperature
D. heating always causes all solids to become insoluble
Show Answer & Explanation

Answer: (C) the solubility of most solids increases with rising temperature

Explanation:
As water temperature increased from 50 °C to 70 °C, progressively more undissolved baking soda dissolved, demonstrating that solubility of solids generally increases with temperature—a core finding stated in the chapter.

Question: According to the chapter, the mixture of gases making up Earth's atmosphere represents which type of mixture?
A. a non-uniform mixture visible to the naked eye
B. a saturated solution incapable of holding more components
C. a uniform mixture that qualifies as a solution
D. a solid dispersed in a liquid
Show Answer & Explanation

Answer: (C) a uniform mixture that qualifies as a solution

Explanation:
The chapter notes that air is a mixture and confirms that a mixture of gases in water is uniform because gases dissolve evenly. By extension, the atmospheric mixture of different gases is also a uniform mixture or solution.

Question: A stone sculpture has a mass of 225 g and occupies a volume of 90 cm³. Based on these measurements and knowledge that water has a density of 1 g/cm³, which statement best predicts the sculpture's behaviour in water?
A. it will sink because its density exceeds that of water
B. it will float because the volume is less than the mass
C. it will remain suspended at mid-depth in water
D. its behaviour depends on the depth of water present
Show Answer & Explanation

Answer: (A) it will sink because its density exceeds that of water

Explanation:
The density of the sculpture is 225 g ÷ 90 cm³ = 2.5 g/cm³, which is greater than water's density of 1 g/cm³. Objects denser than the liquid they are placed in will sink.

Question: During Activity 9.7, when a stone tied with thread is slowly lowered into water in a measuring cylinder initially showing 50 mL, the water level rises to 55 mL. This rise in water level represents what quantity?
A. the mass of the stone in grams
B. the volume displaced by the stone in cubic centimetres
C. the density of the stone relative to water
D. the solubility of the stone material
Show Answer & Explanation

Answer: (B) the volume displaced by the stone in cubic centimetres

Explanation:
Subtracting the initial volume (50 mL) from the final volume (55 mL) gives 5 mL of water displaced, which equals the volume of the object. Since 1 mL of water displaced equals 1 cm³, the stone's volume is 5 cm³.

Question: Asima Chatterjee's pioneering work on medicinal plants involved extracting and isolating compounds using solvents and solutions. What does this application suggest about the usefulness of understanding solubility and dissolution?
A. solvents are only useful in academic chemistry laboratories
B. controlling which substances dissolve in which solvents enables extraction of specific compounds from natural materials
C. all plant compounds dissolve equally well in water
D. solubility has no practical application outside of food preparation
Show Answer & Explanation

Answer: (B) controlling which substances dissolve in which solvents enables extraction of specific compounds from natural materials

Explanation:
By using different solvents to extract and isolate specific compounds from medicinal plants, Chatterjee's work demonstrates that understanding solubility allows scientists to selectively dissolve desired compounds while leaving others behind—a practical application of solution chemistry principles.

Question: Water at 4 °C possesses its highest density among all temperatures. When water cools further and freezes into ice at 0 °C, the particles arrange themselves to occupy more space. Which consequence of this structural change is most significant for aquatic life?
A. ice becomes denser and sinks to the bottom of lakes
B. ice forms a floating layer that insulates water below, preventing it from freezing solid
C. water loses all dissolved oxygen upon freezing
D. aquatic organisms are forced to migrate to warmer regions
Show Answer & Explanation

Answer: (B) ice forms a floating layer that insulates water below, preventing it from freezing solid

Explanation:
Because the expanded ice structure causes its density to drop below liquid water's density, ice floats and forms an insulating layer on top of lakes and oceans. This floating layer protects the liquid water underneath from freezing completely, preserving habitat for fish and other organisms beneath the surface.

Question: In the traditional salt production method described in Ningel village, Manipur, salty water is extracted and then boiled in large metal pans until water evaporates and salt crystals form. This process demonstrates which property of solutions?
A. that all solutes dissolve equally in any solvent
B. that heating a solution prevents further dissolution
C. that a solute can be recovered from a solution by evaporating the solvent
D. that solvents cannot be separated from solutes once mixed
Show Answer & Explanation

Answer: (C) that a solute can be recovered from a solution by evaporating the solvent

Explanation:
Boiling the salt solution causes the solvent (water) to evaporate, leaving behind the dissolved solute (salt) in crystalline form. This illustrates that components of a solution can be separated by removing the solvent through heat—a practical demonstration of solution chemistry.

Question: When coloured liquids are measured in a measuring cylinder, the instruction states that the mark should coincide with the top of the meniscus, whereas for colourless liquids the mark should coincide with the bottom. What explains this difference in reading technique?
A. coloured and colourless liquids have different densities
B. the meniscus shape changes depending on liquid colour
C. the visual clarity of coloured liquids makes their top surface the easiest to read accurately
D. pressure affects coloured liquids differently than colourless ones
Show Answer & Explanation

Answer: (C) the visual clarity of coloured liquids makes their top surface the easiest to read accurately

Explanation:
For colourless liquids like water, the bottom of the curved meniscus is easiest to see and read accurately. For coloured liquids, the colour makes the top of the meniscus more visible and readable. The measurement technique is adapted to whichever part of the meniscus can be most clearly observed.

Question: Reema moulded her 120 g piece of clay into a compact cube of 60 cm³, then flattened it into a thin sheet. Without changing the amount of clay, what will happen to its density after flattening?
A. density will increase because the sheet is thinner
B. density will decrease because the volume increases when the clay is spread out
C. density will remain exactly the same because mass and the substance have not changed
D. density will become impossible to calculate
Show Answer & Explanation

Answer: (C) density will remain exactly the same because mass and the substance have not changed

Explanation:
Density depends only on the ratio of mass to volume. Although flattening the clay changes its shape and increases its volume, the mass remains 120 g. The ratio will still be the same: density = 120 g ÷ (new, larger volume) yields the original density value regardless of shape, since both mass and the material composition remain constant.

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