Which clue can be used to identify a chemical reaction as a replacement reaction? the reaction has two reactants with ions that seem to switch places. the reaction has a single reactant that changes into two or more products. the reaction involves oxygen reacting with a hydrocarbon and giving off heat. the reaction involves a single product forming from two or more reactants.

Option (a) is the correct answer.

Explanation:

When only one element gets displaced upon chemical reaction between a compound and an element then it is known as a single replacement reaction.

For example,

On the other hand, when two compounds chemically react together and their ions get replaced by each other then it is known as a double replacement reaction.

For example,  

Thus, we can conclude that the reaction which has two reactants with ions that seem to switch places clue can be used to identify a chemical reaction as a replacement reaction.

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c)as speed changes, wavelength and frequency change.

everything changes!