Question

how to prove more reactive element displaces less reactive element

Answer 1

Hey there,

You can prove this performing a simple reaction between a metal compound and a pure metal.
Say you have Silver Sulfate and a copper wire readily available.

Prepare a silver sulfate solution and place the copper wire inside the solution.
Leave the solution aside for sometime.
After an hour or half you can notice the color of solution turning from light yellow to blue. 
This is because of the displacement reaction between copper and silver.
You can also notice precipitate of silver in the copper wire.
Therefore you get,

Silver Sulfate+Copper= Copper Sulfate+ Silver

Notice in the below attachment that copper is more reactive than silver.

Hope this helps...