CBSE Class 9 Science Chapter 05 Exploring Mixtures And Their Separation MCQs Set 01

Answer: (A) Because ORS depends on a fixed proportion of solute to solvent, and changing this ratio changes the concentration

Explanation:
The chapter uses ORS to show that concentration is fixed by the exact proportion of solute to solvent; altering the amount of salt, sugar or water gives a different solution, not ORS anymore.

Answer: (B) 100 mL of vinegar contains 5 mL of acetic acid

Explanation:
Volume by volume percentage compares the volume of solute to the total volume of solution, so 5% v/v means 5 mL of acetic acid is present in every 100 mL of vinegar, since both acetic acid and water are miscible liquids.

Answer: (B) Because measuring a liquid's volume is quicker and easier than weighing it in clinical settings

Explanation:
The chapter notes that % m/v is used where volume is easier to measure than mass, such as in hospitals and laboratories, making it convenient for liquid medicines like glucose drips.

Answer: (B) B's solubility increases more sharply with rising temperature compared to A's

Explanation:
A steeper solubility curve simply means solubility rises faster with temperature for that compound; this is exactly the kind of comparison made between compounds A and B in the chapter's solubility curve activity.

Answer: (B) To remove insoluble impurities so that only pure crystals form on cooling

Explanation:
Filtering the hot solution takes out solid impurities that did not dissolve, ensuring that when the filtrate cools slowly, the crystals that separate out are pure copper sulfate rather than contaminated with debris.

Answer: (B) Acetone has a much lower boiling point than water, so it vaporises first and can be condensed separately

Explanation:
Since acetone boils around 56 degrees C while water boils at 100 degrees C, heating the mixture makes acetone vapourise well before water does; this vapour is then cooled in a condenser and collected as pure acetone, leaving water behind in the flask.

Answer: (B) The components have boiling point differences smaller than about 25 degrees C

Explanation:
Simple distillation suits liquids differing by at least roughly 25 degrees C in boiling point, but petroleum fractions have closer boiling points, so fractional distillation is used instead, as described for the refinery process.

Answer: (B) So capillary action can draw the water upward through the paper and carry the ink components along without washing the spot away immediately

Explanation:
If the spot were submerged directly in water, the ink would simply dissolve into the liquid instead of travelling up the paper; keeping the spot above the water surface lets the rising solvent gradually carry the different coloured components at different speeds, separating them.

Answer: (B) Two immiscible liquids that form separate layers due to density differences

Explanation:
The mustard oil and water activity shows that immiscible liquids settle into distinct layers based on density, and a separating funnel with a stopcock lets the denser lower layer be drained off first while the upper layer stays behind.

Answer: (B) Sublimation involves a solid changing directly to vapour without passing through the liquid state, unlike evaporation which involves a liquid turning to vapour

Explanation:
Camphor, on gentle heating below its melting point, converts straight from a solid into vapour, bypassing the liquid stage entirely, which is the defining feature separating sublimation from evaporation of liquids.

Answer: (B) Because brass is an alloy, a homogeneous mixture of metals formed at high temperature, and its components cannot be separated by physical means

Explanation:
Alloys like brass form when metals are melted together and then solidify into a uniform new material; the chapter states clearly that physical separation methods do not work on alloys because the metals are locked into a homogeneous blend.

Answer: (C) Coagulation, using a substance such as alum

Explanation:
• Filtration alone cannot remove very fine particles causing cloudiness
• Alum acts as a coagulant, making tiny suspended particles stick together into bigger clumps
• These clumps then settle down by gravity and can be removed by decantation or filtration

Answer: (B) The rapid spinning generates an outward force that pushes heavier particles to settle faster than gravity alone would allow

Explanation:
Spinning a sample at high speed creates a centrifugal force much stronger than gravity, so denser components like blood cells are forced outward and settle at the bottom of the tube far more quickly than if the sample were merely left undisturbed.

Answer: (B) It is a colloid, since its dispersed particles are large enough to scatter light despite appearing homogeneous

Explanation:
A visible light path indicates scattering, known as the Tyndall effect, which occurs in colloids and suspensions but not true solutions; since the mixture still looks uniform, it fits the description of a colloid like milk rather than a suspension with visibly settling particles.

Answer: (B) Suspension particles are larger than 1000 nm, colloid particles range between 1 and 1000 nm, and solution particles are smaller than 1 nm

Explanation:
The chapter ranks particle sizes clearly: dissolved particles in a true solution are smallest, colloidal particles are intermediate, and suspended particles are the largest, which explains why suspensions settle while colloids and solutions remain dispersed.

Answer: (A) Water, because it is the substance that dissolves the sugar

Explanation:
The solvent is simply the substance that does the dissolving, while the solute is what gets dissolved. Water plays that dissolving role for sugar, so it is the solvent regardless of relative amounts.

Answer: (B) Immiscible

Explanation:
Liquids that refuse to mix and instead form distinct layers, like oil and water, are called immiscible. This is different from miscible liquids such as acetone and water, which blend completely.

Answer: (B) Mustard oil is less dense than water

Explanation:
Since mustard oil floats above the water instead of sinking, it must be lighter, i.e., less dense, than water. Density difference is exactly what makes separating funnels work for immiscible liquids.

Answer: (A) 3, 2, 1, 4

Explanation:
• First a hot saturated solution of copper sulfate is made by dissolving the salt in heated water.
• This hot solution is then filtered to remove insoluble impurities.
• The clear filtrate is left to cool slowly, allowing crystals to form.
• Finally, the crystals are filtered out, rinsed and dried.

Answer: (B) To separate fragrance and flavour components from plant parts and support local perfume businesses

Explanation:
The centre extracts flavour and fragrance compounds from flowers, leaves and other plant parts, and also helps farmers grow fragrance plants and guides people setting up perfume businesses. It has nothing to do with petroleum refining or water purification.

Answer: (C) He developed and implemented the ORS treatment for dehydration caused by diseases like diarrhoea

Explanation:
Mahalanabis formulated the Oral Rehydration Solution therapy that transformed how dehydration from cholera and diarrhoea is treated, a contribution later popularised worldwide by the WHO.

Answer: (B) A homogeneous mixture of two or more metals, or a metal and a non-metal, formed by melting and cooling

Explanation:
Metals will not mix at ordinary room temperature; they must first be melted together and then allowed to solidify. The resulting uniform material, such as brass or stainless steel, cannot be split back into its metals by ordinary physical methods.

Answer: (B) Coagulant

Explanation:
A substance that causes fine particles to clump and settle out of a heterogeneous mixture is called a coagulant, and the overall process is coagulation. Lemon juice acting on milk to form paneer works on the same principle.

Answer: (C) Colloid

Explanation:
Particles that neither dissolve completely like in a true solution nor settle out quickly like in a suspension, but stay dispersed while still scattering light, fall in the colloidal size range. Clouds behave exactly this way, which is why they can appear hazy or glowing under sunlight.

Answer: (B) 4% m/v

Explanation:
Mass by volume percentage is worked out as (mass of solute divided by volume of solution) multiplied by 100, which here gives (8/200) x 100 = 4% m/v.