we know that the arrangement of metals in order of increasing strength of reducing agent is Cu<Fe<Zn<Al<Mg .

but in the experiment electrochemical cells,the result that i got was
Cu<Fe<Al<Zn<Mg ?? why ??

The arrangement of metals in order of increasing strength of reducing agent is based on their standard reduction potentials. However, in electrochemical cells, several factors can affect the observed results, including concentration, temperature, and the specific setup of the cell.

One possible explanation for the different result you obtained in your experiment is the effect of concentration. The concentration of the metal ions in the electrolyte solution can influence the flow of electrons and the overall reaction rate. If the concentration of the metal ions was higher for aluminum (Al) and zinc (Zn) compared to copper (Cu), iron (Fe), and magnesium (Mg), it could result in a higher observed reducing ability for Al and Zn.

Other factors that could contribute to the discrepancy include the nature of the electrodes used in the experiment and the presence of any impurities or contaminants. Some metals, such as aluminum, may form a protective oxide layer on their surface, which can affect their reactivity in the electrochemical cell.

To further investigate and understand the results obtained in your experiment, you could consider repeating the experiment with controlled and equal concentrations of metal ions, ensuring the use of clean and identical electrodes, and verifying the correct setup and connections of the electrochemical cell. Additionally, consulting relevant literature and comparing your experimental results with standard reduction potentials can help in understanding the observed discrepancy and any potential variations in the reactivity of the metals.