NCERT Class-9 Science Solutions: Chapter 3-Atoms And Molecules Part 5

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Question 19:

What is the fraction of the mass of water due to neutrons?


Question 20:

Does the solubility of a substance change with temperature? Explain with the help of an example.


Yes, it is a temperature dependent property. The solubility generally, increases with increase in temperature. For example, you can dissolve more sugar in hot water than in cold water.

Image of Solubility

Image of Solubility

Image of Solubility

Question 21:

Classify each of the following on the basis of their atomicity.


  1. 2

  2. 3

  3. 3

  4. 8

  5. 4

  6. 4

  7. 14

  8. 3

  9. 2

  10. 5

  11. 1 (Noble gases do not combine and exist as monoatomic gases)

  12. Polyatomic. It is difficult to talk about the atomicity of metals as any measurable quantity will contain millions of atoms bound by metallic bond (about which you would learn later).

Question 22:

You are provided with a fine white coloured powder which is either sugar or salt. How would you identify it without tasting?


On heating the powder, it will char if it is a sugar.

Alternatively, the powder may be dissolved in water and checked for its conduction of electricity. If it conducts, it is a salt.

Question 23:

Calculate the number of moles of magnesium present in a magnesium ribbon weighing. Molar atomic mass of magnesium is .


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