NCERT Class-9 Science Solutions: Chapter 3-Atoms and Molecules Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 15:

Give the formulae of the compounds formed from the following sets of elements

  1. Calcium and fluorine
  2. Hydrogen and sulphur
  3. Nitrogen and hydrogen
  4. Carbon and chlorine
  5. Sodium and oxygen
  6. Carbon and oxygen


Question 16:

Which of the following symbols of elements are incorrect? Give their correct symbols

  1. Cobalt
  2. Carbon
  3. Aluminium
  4. Helium
  5. Sodium


  1. Incorrect, the correct symbol of cobalt is
  2. Incorrect, the correct symbol of carbon is
  3. Incorrect, the correct symbol of aluminium is
  4. Correct
  5. Incorrect, the correct symbol of sodium is

Question 17:

Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them.

  1. Ammonia
  2. Carbon monoxide
  3. Hydrogen chloride
  4. Aluminium fluoride
  5. Magnesium sulphide


Chemical Formulae

Question 18:

State the number of atoms present in each of the following chemical species