2.3.1 Write down the chemical formula of the substance in which the ratio is:

2.3.1 Write down the chemical formula of the substance in which the ratio is:

• a) 1:1

  • For NaCl (Sodium chloride), the ratio of Na:Cl atoms is 1:1.
  • Answer: $\boxed{\text{NaCl}}$

• b) 2:1

  • For H$_2$O (Water), the ratio of H:O atoms is 2:1.
  • Answer: $\boxed{\text{H}_2\text{O}}$

• c) 1:2

  • For CO$_2$ (Carbon dioxide), the ratio of C:O atoms is 1:2.
  • Answer: $\boxed{\text{CO}_2}$

• d) 2:1:4

  • For H$_2$SO$_4$ (Sulphuric acid), the ratio of H:S:O atoms is 2:1:4.
  • Answer: $\boxed{\text{H}_2\text{SO}_4}$

2.3.2 What is the ratio in CaCO$_3$?

• In the chemical formula CaCO$_3$:
  • There is 1 Calcium (Ca) atom.
  • There is 1 Carbon (C) atom.
  • There are 3 Oxygen (O) atoms.
• The ratio of Ca:C:O atoms is 1:1:3.
• Answer: $\boxed{\text{1:1:3}}$