2.30 Describe how reactions with water and dilute acids can be used to deduce the following order of reactivity: potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper

Potassium, sodium, calcium and lithium all react with water, and very vigorously with acid. Calcium has a much less vigorous reaction.

Magnesium, zinc and iron react with acid and very slowly with water. 

Copper reacts with neither (boring!).

By watching their chemical reactions, we can put them into order of reactivity:

• Potassium
• Sodium
• Lithium
• Calcium
• Magnesium
• Zinc
• Iron
• Copper

Potassium + water ;)