The reaction takes place in which beaker?

 

 

 

The reaction take place only in beaker A.

When iron nail is dipped in copper sulphate solution, the colour of copper sulphate tuns from bule to light green and reddish brown deposits is formed on iron nail. This is because iron is more reactive than copper, so it displaces Cu from ${\mathrm{CuSO}}_4.$ Solution. 

The displacement reaction can be written as ${\mathrm{CuSO}}_4+\mathrm{Fe}\to {\mathrm{FeSO}}_4+\mathrm{Cu}$