1. What conditions are needed for iron to rust?
- Water and oxygen
- Nitrogen alone
- Dry oxygen alone
Check the answer and reasoning
Water and oxygen
Both water and oxygen are needed for ordinary rust formation.
CHEM / IGCSE
Periodic chemistry, resources and environment
Group trends connect electron arrangement with reactivity. Halogens can displace less reactive halide ions; noble gases are relatively unreactive. Transition metals often act as catalysts and form coloured compounds.
Learning objectives
- Explain periodic chemistry, resources and environment using a concrete example.
- Apply the worked method and justify each step.
- Recognise the limitation described in the final check.
The big idea
Group trends connect electron arrangement with reactivity. Halogens can displace less reactive halide ions; noble gases are relatively unreactive. Transition metals often act as catalysts and form coloured compounds.
Metal extraction, rusting, air pollutants, water treatment and fertilisers show chemistry at environmental scale. Distinguish the greenhouse effect from ozone depletion and evaluate resource use with evidence, not a single benefit.
Worked example
Which halogen displaces bromide ions: chlorine or iodine?
Follow the solution
Chlorine is more reactive than bromine and oxidises bromide to bromine.
Investigate and explain
Predict the worked result before calculating. Change one input, record the new result, and explain which assumptions still hold.
Related interactive model. Compare its assumptions with the explanation; it is not a complete syllabus lesson.
Check your understanding
2. Which halogen displaces bromide ions: chlorine or iodine?
- Iodine
- Chlorine
- Both equally
Check the answer and reasoning
Chlorine
Chlorine is more reactive than bromine and oxidises bromide to bromine.
3. Does potable water have to be chemically pure H₂O?
- Yes
- Only if filtered
- No
Check the answer and reasoning
No
Drinking water must be safe but may contain dissolved ions; purity is a different criterion.