NCERT Solutions Curiosity Chapter 9 Science • Society • Interdisciplinary Projects — Discover, design, and debate

Book page 151 Updated on2026-09-05

Q1.

Research project on Dead Sea: Why is there no aquatic life in the Dead Sea? Try to find out if there are any other similar water bodies.

Answer

How to do the project: collect the salt content, the density and the temperature of the Dead Sea from an atlas or an encyclopaedia, compare them with ordinary sea water, and then explain the biology from the chemistry. Present it as a one-page report with a comparison table and a map.

Sample answer:

The Dead Sea is not really a sea but a landlocked lake between Israel and Jordan. Rivers bring dissolved salts into it, but it has no outlet, and the desert sun evaporates the water fast. Evaporation removes the solvent and leaves the solute behind, so over thousands of years the water has become an extremely concentrated salt solution — close to saturated, and roughly ten times as salty as ordinary sea water.

Almost nothing can live in it, for three reasons:

The solution is too concentrated for living cells. A fish or a plant placed in it loses water from its cells into the surrounding solution and cannot survive.
Very little oxygen dissolves in it. A liquid already crowded with dissolved salt has little room left for dissolved gas, and the water is warm — and warm water holds less oxygen anyway.
No plants can grow in it, so there is no food chain to support animals.

Only some microbes survive there, which is why the lake is called "dead". Its very high density — noticeably greater than that of the human body — is also why a swimmer floats on it without effort.

Water body	Where	Why it is similar
Great Salt Lake	Utah, USA	Landlocked, no outlet, very high salt content; only brine shrimp and algae survive
Lake Assal	Djibouti, Africa	One of the saltiest lakes on Earth; salt is mined from its shores
Sambhar Salt Lake	Rajasthan, India	India's largest inland salt lake; salt is produced by evaporating its water
Lonar Lake	Maharashtra, India	A crater lake, both salty and alkaline; very few organisms live in it
Pangong Tso	Ladakh, India	A high-altitude salt lake with almost no fish

The common cause: every one of these is a closed basin — water flows in, carrying dissolved salts, but leaves only by evaporation, which carries no salt away. The concentration can therefore only go up.

Q2.

Investigate how well common salt dissolves in different solvents, such as water, vinegar, and oil. Compare the solubility of salt in each solvent and record your observations.

Answer

Method — keep everything the same except the solvent. Take three clean transparent glasses and put 50 mL of water in the first, 50 mL of vinegar in the second and 50 mL of cooking oil in the third, all at room temperature. Add one level teaspoon of common salt to each, stir for the same length of time with a clean spoon, and observe. Keep adding spoonfuls until salt stops dissolving, counting as you go. Record everything in a table.

Solvent (50 mL)	What you observe	Roughly how many spoons dissolve	Conclusion
Water	Salt disappears; liquid stays clear	3 to 4	Dissolves very well
Vinegar	Salt disappears, slightly more slowly	About 3	Dissolves well — vinegar is mostly water
Cooking oil	Grains stay whole and settle at the bottom, however long you stir	None	Does not dissolve at all

Why the results come out this way: Salt dissolves only when the solvent's particles can pull the salt particles off the crystal and hold them apart. Water particles can do this. Vinegar is a solution of acetic acid in water, so it behaves almost like water, though the dissolved acid takes up a little of the water's capacity. Oil particles have no such pull at all, so the crystal is never broken up — the salt simply lies in the oil unchanged.

Check it yourself: Use the same spoon, level it off each time, and stir for the same count in every glass. If you change two things at once you cannot say which one caused the difference — that is the whole point of a fair test.

Q3.

Debate in class — Is water truly the most versatile solvent?

Answer

How to run the debate: divide the class into two sides, give each ten minutes to collect examples, and insist that every point be supported by an example rather than an opinion. Judge on evidence, not on volume.

Yes — water is the most versatile solvent	No — it is not the most versatile
It dissolves an enormous range of substances — salts, sugars, ORS powder, many medicines, and gases such as oxygen and carbon dioxide.	It cannot dissolve oils, fats, wax, plastics, or most paints and varnishes — which is why oil paint has to be thinned with turpentine, not water.
It carries dissolved substances through every living thing — sap in plants, blood in animals, digested food in your intestine.	Some drug compounds come out of a herb only with alcohol or with a hydro-alcoholic mixture, as the chapter's own heritage box notes.
It is cheap, plentiful, non-poisonous and does not catch fire — an industrial solvent that is also safe to drink.	Traditional Indian medicine also uses oil, ghee and milk as solvents where water will not do the job.
Life itself began and still runs in water because of this.	"Most versatile" cannot be settled in the abstract — the best solvent is the one that dissolves the substance you actually need to dissolve.

The strongest position: Water is rightly called the universal solvent, and no other single liquid dissolves anything like the same range of everyday substances. But "universal" is a compliment, not a fact — grease on a plate needs soap, oil paint needs turpentine, and a chemist chooses a solvent to fit the job. Water is the most versatile solvent we have, and it is still not enough on its own.

Tip: The best debating point on either side is a concrete example the other side cannot explain away. Bring one from your own kitchen.

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