NCERT Solutions Curiosity Chapter 9 –174River pollution, churning at the dhaba, and the carpenter’s magnet — In-text Questions

Book page 173 Updated on2026-09-05

Q1.
Let us raise awareness about the issues related to river and ocean pollution by composing a poem. A few lines have been written here, add more lines—
Answer

What your poem should carry: what the pollution is (plastic bags, bottles, wrappers, straws), who it hurts (fish like Koilas, birds, and us), where it comes from (our own homes and streets) and what we can do (refuse single-use plastic, never throw waste into water, pick up what we see).

Sample answer — lines you can add to the book’s poem:

A bottle cap, a broken straw,
A wrapper from a shop next door,
The drain took it, the river too,
And left it at the ocean floor.

Koilas cannot tell the tale,
Of nets that catch both fish and mail —
Of packets, bags and plastic string,
Caught up in the fisherman’s haul.

So carry a cloth bag to the store,
Refuse the plastic at the door,
For every piece we do not throw,
Is one less pain the rivers know.
The link with this chapter: Otukkam’s fishing net separates fish from water — a natural kind of filtration. But the net also brings up bags, bottles and wrappers, because plastic does not dissolve and does not rot. Nature has no separation method that can take plastic out of a river. The only method that works is not putting it in.
Q2.
A bowl of milk in your home has gone sour. Discuss with your parents how you can use it in another way. Also, which method of separation will you use in the process?
Answer

Sour milk is not waste. In Indian kitchens it is put to work at once.

Use it forWhat is doneMethod of separation
Paneer or chhenaThe milk curdles; the solid chhena is poured into a muslin cloth and the whey drains awayFiltration (through cloth)
Butter and buttermilkSet it into curd and churn with a mathni; butter floats to the topChurning
Kadhi, dhokla, idli batter, sour-milk parathaUsed directly for its sournessNo separation needed
Whey for kneading dough or watering plantsThe liquid left after making paneer is kept and usedAlready separated by filtration
The main method here is filtration. Sour milk splits into a solid part (chhena) and a liquid part (whey). Pouring it through a muslin cloth holds the solid back — the chhena is the residue, the whey is the filtrate. If instead you set the milk into curd and churn it, the lighter butter separates and floats, which is churning.
Tip: Squeeze the cloth gently, hang it for half an hour and press the chhena under a weight. You get fresh paneer — and you have used filtration and decantation without leaving the kitchen.
Q3.
Can you name one kitchen appliance which runs on electricity that is used to prepare buttermilk?
Answer

An electric mixer–grinder (the mixie), or a purpose-made electric churner / butter-churner (electric mathni). A hand blender does the same job.

Curd in the mixer jar → the blades churn it rapidly
→ fat globules join together and, being lighter, rise and float as butter
→ the liquid left below is chhach (buttermilk)
Why churning separates butter: the fat in curd is present as countless tiny globules spread through the liquid. Churning knocks them together until they form lumps big enough to see. Because fat is less dense than the watery part, these lumps float to the top and can be lifted off.
Did you know? The traditional mathni (or ravi) with a rope wound round it does exactly the same thing without any electricity — and the big wooden churn in the dhaba painting is its village-sized cousin.
Q4.
Which method of separation did the carpenter use? Recall the chapter ‘Exploring Magnets’.
Answer

He used magnetic separation — moving a magnet through the sawdust so that all the iron nails jumped up and stuck to it.

ComponentBehaviour near a magnetCalled
Iron nailsStrongly attracted, cling to the magnetMagnetic substance
SawdustNot attracted at all, stays behindNon-magnetic substance
Why it beats handpicking here: the carpenter had begun picking the nails out by hand. But nails buried in sawdust are hard to see and sharp to touch. A magnet finds every one of them in a single sweep, including the ones out of sight — it uses a property (difference in magnetic properties) that the eye cannot judge.
Did you know? Recyclers use giant electromagnets fitted to cranes to pull scrap iron out of heaps of mixed waste. The scrap iron is then melted and used again.
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