错误做法:

Using the order Li > Na > K instead of the Edexcel-specified K > Na > Li

原因:

Edexcel explicitly requires the K > Na > Li order, so you will lose marks for incorrect ranking.

正确做法:

Memorise the exact spec reactivity order: K, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au.

错误做法:

Predicting displacement when the added metal is less reactive than the metal in the salt/oxide

原因:

Displacement only occurs if the added metal is higher in the reactivity series than the metal ion present.

正确做法:

Always check the reactivity order before predicting displacement reactions.

错误做法:

Stating rusting only requires water or only requires oxygen

原因:

Both water and oxygen are essential for rusting to occur, as rust is hydrated iron(III) oxide.

正确做法:

Recall that both $H_{2}O$ and $O_2$ must be present for iron to rust; removing either stops rusting.

错误做法:

Confusing oxidising and reducing agents: stating the oxidising agent is oxidised

原因:

Oxidising agents cause oxidation in other substances, so they are themselves reduced.

正确做法:

Remember: reducing agent = oxidised; oxidising agent = reduced.

错误做法:

Forgetting state symbols in displacement reaction equations

原因:

Edexcel exam questions often explicitly award marks for correct state symbols.

正确做法:

Always include (s), (l), (g), (aq) for all reactants and products in balanced equations.

错误做法:

Thinking galvanising only works as a barrier method

原因:

If the zinc coating is scratched, zinc is more reactive than iron so it acts as a sacrificial metal, continuing to protect the iron.

正确做法:

Remember galvanising provides both barrier and sacrificial protection.