Q25 of 61 Page 1

When you add about 2 mL of acetic acid to a test tube containing an equal amount of distilled water and leave the test tube to settle after. shaking its contents, then after about 5 minutes what will you observe in the test tube:

The correct answer is: option (b).

On addition of acetic acid to equal amount of distilled water, the solution obtained will be a clear colorless solution. This is because acetic acid is immiscible in water and therefore the solution is clear and colorless.

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23

(a) List three common refractive defects of vision. Suggest the way of correcting these defects.

(b) About 45 lac people in the developing countries are suffering from corneal blindness.


About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people?

 24

The position of three elements A, B and C in the Periodic Table are shown below:





















































Group



I



II



III



IV



V



VI



VII



Period










1



B









2









A



3








C




Giving reasons, explain the following:


(a) Element A is a non-metal.


(b) Atom of elements C has a larger size than atom of element A.


(c) Elements B has a valency of 1.

 26

In order to study saponification reaction we first prepare 20% solution of sodium hydroxide. If we record the temperature of this solution just after adding sodium hydroxide flakes to water and also test its nature using litmus, it may be concluded that the process of making this solution is to

 27

While studying saponification reaction for the preparation of soap, the teacher suggested to a student to add a small quality of common salt to the reaction mixture. The function of common salt in this reaction is to: