CBSE Class 8 Science Chapter 09 The Amazing World Of Solutes, Solvents, And Solutions MCQs Set 01

Answer: (B) Uniform mixture

Explanation:
According to the chapter, when salt and sugar dissolve in water, the components are evenly distributed throughout, forming a uniform mixture called a solution.

Answer: (C) Because water is present in a smaller quantity than sugar

Explanation:
The chapter explicitly states that in solutions formed by mixing two liquids (or a liquid and solid), the substance present in smaller amount is called the solute while the one in larger amount is called the solvent—which explains why water remains the solvent in chashni.

Answer: (B) An unsaturated solution can dissolve more solute at a given temperature

Explanation:
The chapter defines unsaturated solution as one in which more solute can be dissolved at a given temperature, whereas a saturated solution is one where no more solute can dissolve at that particular temperature.

Answer: (B) Solubility increased as temperature increased

Explanation:
• At 20 °C, less baking soda dissolved
• At 50 °C, more baking soda dissolved
• At 70 °C, even more baking soda dissolved
• This demonstrates that for most substances, solubility increases with increasing temperature.

Answer: (A) Gases dissolve less in cold water than in warm water

Explanation:
The chapter states that the solubility of gases generally decreases as temperature increases, meaning more oxygen dissolves in cold water, which ensures sufficient oxygen for aquatic life.

Answer: (B) Density

Explanation:
Density is defined in the chapter as the mass present in a unit volume of a substance, and is expressed mathematically as Density = Mass/Volume.

Answer: (B) To provide better accuracy in volume measurement due to smaller divisions per unit height

Explanation:
The narrow, tall design allows for smaller divisions and better measurement precision—a change in liquid level is more noticeable in a narrow cylinder, allowing more accurate readings compared to a wide container.

Answer: (B) 2.7 (unitless number)

Explanation:
The chapter defines relative density as the density of a substance divided by the density of water. Since aluminum's density is 2.7 g/cm³ and water's is 1 g/cm³, the relative density is 2.7, which is expressed as a unitless number.

Answer: (B) The particles in ice arrange to occupy more space, decreasing its density below that of liquid water

Explanation:
The chapter explains that water has a special property—its density is highest at 4 °C. When water freezes, it undergoes expansion as particles arrange themselves in a way that takes up more space, making ice less dense than liquid water, so it floats.

Answer: (B) Density increases as particles move closer together

Explanation:
According to section 9.5.3, increasing pressure causes gas particles to move closer together, reducing the gas volume and increasing its density. This effect is much more pronounced in gases than in liquids or solids.

Answer: (C) Density decreases because volume increases while mass stays the same

Explanation:
The chapter explains that as temperature increases, particles spread out causing volume to increase, but mass remains unchanged. Since Density = Mass/Volume, an increase in volume without change in mass results in decreased density.

Answer: (C) Initial water level from final water level

Explanation:
Activity 9.7 describes placing an object in water and recording initial and final volumes. The volume of the object equals the final water level minus the initial water level, representing the water displaced by the object.

Answer: (B) Solubility of gases decreases with increasing temperature

Explanation:
The chapter states that solubility of gases generally decreases as temperature increases, meaning warm water holds less dissolved oxygen, which can threaten aquatic life that depends on this oxygen for survival.

Answer: (B) Kilogram per cubic metre (kg/m³)

Explanation:
The chapter specifies that since SI units of mass and volume are kilogram (kg) and cubic metre (m³) respectively, the SI unit of density must be kilogram per cubic metre, abbreviated as kg/m³.

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

Explanation:
Density of stone = 16.4 g ÷ 5 cm³ = 3.28 g/cm³. Since this is greater than water's density of 1 g/cm³, the stone will sink. Objects denser than water sink while those less dense float.

Answer: (B) Water, because it is the liquid component that dissolves the solid

Explanation:
Even when a solid solute is present in much larger quantity than the liquid, the liquid component remains the solvent by definition. The chapter explicitly explains this through the example of Gulab jamun chashni, where despite sugar being abundant, water is still called the solvent because it is the dissolving medium.

Answer: (C) The solution had become saturated at that particular temperature

Explanation:
Once solid solute begins to settle at the bottom without dissolving further, the solution has reached saturation—meaning no more solute can dissolve at that temperature. The chapter defines this state clearly and contrasts it with unsaturated solutions where more solute can still be dissolved.

Answer: (B) Higher temperature increased the solubility of baking soda in water for most substances

Explanation:
The experiment demonstrated that solubility of most substances increases with temperature. As water was heated, it could dissolve more baking soda—what was a saturated solution at 50 °C became unsaturated at 70 °C.

Answer: (C) Cold water can dissolve more oxygen gas than warm water

Explanation:
• The chapter states gas solubility generally decreases as temperature increases
• More oxygen dissolves in cold water, which is crucial for aquatic life
• This is opposite to the trend observed for solid solutes in liquids.

Answer: (B) The oil is less dense than water because it is lighter for the same volume

Explanation:
Since 1 litre of water (1000 mL) weighs approximately 1000 grams, but 1 litre of oil weighs only 910 grams, the oil has less mass in the same volume. This means oil is less dense than water, which is why oil floats on water as shown in figures throughout the chapter.

Answer: (C) 10 divisions

Explanation:
The volume difference between 10 mL and 20 mL is 10 mL. If each small division reads 1 mL, then 10 mL ÷ 1 mL per division = 10 divisions. Activity 9.4 guides students through this exact calculation to determine the precision of a measuring cylinder.

Answer: (C) The density will remain the same because it is the same piece of clay

Explanation:
Density depends only on mass and volume, not on shape. When Reema flattens the clay, she does not add or remove material—both mass and volume remain unchanged, so the density stays constant.

Answer: (B) The water expanded because its density decreased upon heating

Explanation:
Heating increases the volume of water without changing its mass. Since Density = Mass/Volume, an increase in volume causes density to decrease. The less dense, expanded water rises in the tube, demonstrating the inverse relationship between temperature and density for most substances.

Answer: (B) The peel contains air pockets that make the overall density of the unpeeled orange less than water

Explanation:
The peel has tiny air-filled spaces that increase the total volume without adding significant mass. This makes the average density of the whole unpeeled orange less than water's density, causing it to float. Once peeled, these air gaps are lost, and the denser fruit sinks.

Answer: (B) 76 cm³

Explanation:
Rearranging the density formula: Volume = Mass ÷ Density = 600 g ÷ 7.9 g/cm³ ≈ 75.9 cm³, which rounds to approximately 76 cm³. This calculation applies the mathematical relationship between density, mass, and volume taught throughout the chapter.