Carbon monoxide is a poisonous gas emitted from car exhausts. It can be detected using the reaction: CO + Pd²⁺ (orange) + H₂O → CO₂ + Pd (black) + 2H⁺.

1. aWhat are the main products of combustion of petrol in an efficient car engine? [1]
2. bHow is the poisonous gas carbon monoxide formed in a car engine? [1]
3. cWhat type of chemical reaction is the change from Pd²⁺ to Pd? Give a reason for your answer. [2]
4. dWhat type of chemical reaction is the change from CO to CO₂? Give a reason for your answer. [2]

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