A) Write the electron arrangement (s and p notation) for Na and O. b) Write the formula for Magnesium chloride and Aluminium oxide using valency. c) Balance the chemical equation Fe + O2 -> Fe2O3. d)

$$\boxed{4Fe + 3O_2 \rightarrow 2Fe_2O_3}$$

9. d) State TWO observations when iron reacts with oxygen.

• i. Formation of a reddish-brown solid (rust).
• ii. The iron loses its metallic luster.

10. a) Explain TWO uses of isotopes in medicine and industry.

• i. In medicine, radioactive isotopes like Cobalt-60 are used in radiotherapy to treat cancer by targeting and destroying cancerous cells.
• ii. In industry, isotopes such as Strontium-90 are used in thickness gauging to measure and control the thickness of materials like paper or plastic sheets during manufacturing.

10. b) Describe TWO environmental applications of Chemistry in daily life.

• i. Water treatment: Chemical processes, such as chlorination and flocculation, are used to remove impurities and pathogens from water, making it safe for drinking.
• ii. Air pollution control: Catalytic converters in vehicles use chemical reactions to convert harmful pollutants like carbon monoxide and nitrogen oxides into less harmful substances such as carbon dioxide, nitrogen, and water vapor.