Which of the following could represent a single-replacement reaction?
element + element = compound
compound = element + element
element + compound = element + compound
compound +compound = compound + compound

(C) element + compound = element + compound

Explanation:

A single replacement reaction is a reaction in which an element from a compound is replaced by another element

For example  

B is the element here replaced by A.

A more reactive element only can replace a less reactive element.  

Single-replacement reactions only occur when the element that is doing the replacing is more reactive than the element that is being replaced.

For example  

Here we see Zinc is more reactive than Copper

Hence it replaces Copper and forms Zinc sulphate.

Copper cannot replace Zinc as it is less reactive than Zinc.

We get to know the reactivity of an element by learning the reactivity series and we can predict whether a single replacement reaction will take place or not by knowing it.

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