Class 6 Science, Chapter 9 (NCERT). 15 questions by concept, 10 with pictures. Open “Show answer” for the answer and why.
How to teach this chapter · Common misconceptions & worked visual for this chapter
What can handpicking conveniently achieve when sorting a mixture?
(d) Removing a few visible, easily grasped pieces
Handpicking sorts components by removing individual pieces. It is convenient when those pieces are few, distinguishable and easy to grasp.
A mixture contains puffed rice and rice grains. The parts are to be separated because there is a lighter or heavier nature. Which separation method matches this property?
(d) Winnowing
The rule is that a separation method is chosen according to the property of the components. Here, there is a lighter or heavier nature, so the matching method is Winnowing. Choosing only from the mixture name would ignore the stated property.
What defining action makes a separation process threshing?
(c) Beating grain-bearing stalks to detach grains
Threshing detaches grains from stalks by beating or mechanical action. The tool alone does not define the process. Blowing loose husk away is winnowing.
The diagram shows paths P and Q during winnowing of peanuts and removed peanut skins. Which assignment fits both paths?
(a) P: removed peanut skins; Q: peanuts
The lighter material follows the sideward path with the air. The heavier material follows the downward path.
Husk and rice fall from a soop in a room with still air. What must change for winnowing to separate them?
(b) Air moving across the falling mixture
Moving air carries lighter husk farther than heavier rice. A soop alone cannot provide this separation in still air.
In the drawing, how will the marked material separate from the other particles when this sieve is used?
(d) remains on the sieve
This sieve has holes larger than the fine particles and smaller than the bran and stones. The marked material remains on the sieve.
Why can a sieve separate fine particles from bigger bran or small stones?
(d) Fine particles pass through the holes, while bigger bran or small stones remain on the sieve.
Sieving allows fine particles to pass through the holes of the sieve. Bigger particles such as bran and small stones remain on the sieve. This difference in what passes and what remains separates the parts.
A sequence starts with salt solution in a dish. After heating, salt is left in the dish and water vapour rises. The water vapour later becomes liquid water. What does this sequence show?
(b) Evaporation helps leave salt behind, and condensation changes water vapour into liquid water.
The observed result of heating the salt solution is that salt is left behind when water goes away. This is the role of evaporation. The rule for the final change is that condensation converts water vapour into its liquid state.
A salt solution is heated so that water goes away as water vapour and salt is left behind. The water vapour is then changed into liquid water. Which ordered pair of process ideas is needed to get salt first and liquid water next?
(b) Evaporation leaves the salt behind; condensation changes water vapour into liquid water.
When a salt solution is heated, water goes away and salt is left behind. That step uses evaporation. To get water back as a liquid, water vapour must change into its liquid state, which is condensation.
Tea has been left still for some time, and the tea leaves have settled at the bottom. There is no strainer. What should be done next to separate the tea from most of the tea leaves?
(c) Pour the tea gently into another cup, leaving most tea leaves at the bottom.
When tea is left undisturbed, tea leaves settle at the bottom. The liquid can then be poured gently so that most tea leaves remain settled. This is decantation, and it may not remove every leaf.
Two mixtures are ready to be separated. In mixture A, tea leaves in tea has been left undisturbed and the insoluble solid has settled at the bottom. In mixture B, oil and water have been left undisturbed and have formed separate layers. Which statement is correct?
(d) Both mixture A and mixture B can use decantation.
Mixture A can use decantation after the insoluble solid has settled, because the liquid can be carefully poured off. Mixture B can also use decantation because oil and water form separate layers after being left undisturbed. The two setups are different, but both allow careful pouring off.
Two filters are available for removing smaller particles from muddy water. Filter A has larger pores. Filter B has small pores. Which choice is more suitable?
(c) Filter B, because it has small pores
The choice of filter depends upon the size of the particles to be removed. Smaller particles need a filter with smaller or finer pores. So the filter with small pores is more suitable.
A separation sequence starts with tea with leaves and ends with collected liquid after the solid is held back. The middle step is missing. Which action completes the sequence as filtration?
(c) Pass the mixture through a strainer.
Filtration means passing the mixture through a filter, cloth, filter paper, or strainer. The filter collects the solid and the liquid passes through. Settling and tilting would be decantation, not the missing filtration step.
A sentence says, "When curd is churned, buttermilk floats at the top and butter is left behind." Which sentence corrects it?
(a) When curd is churned, butter floats at the top and buttermilk is left behind.
The sentence has reversed the positions. When curd is churned, butter is separated. Butter, being lighter, floats at the top, while buttermilk is left behind.
Look at the pot shown after curd has been churned. Which substance is the floating top part marked ?
(b) Butter
When curd is churned, butter is separated. The butter, being lighter, floats at the top, while the buttermilk is left behind.
Wrong
Filter paper separates salt from clear salt water.
Why it feels right. The filter traps sand, so it should trap salt as well.
Right
Dissolved salt passes through ordinary filter paper with the water.
Worked example
