Arrange the ions Cu2+ Zn2+ Mg2+ and Al 6+

in order of decreasing ability to be reduced
and in order of decreasing ability to be oxidized

the species most easily reduced have large positive voltage

potentials and the species most easily oxidized have large negative potentials.

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To determine the order of decreasing ability to be reduced, we need to consider the reduction potentials of the ions. The higher the reduction potential, the greater the ability to be reduced.

To determine the order of decreasing ability to be oxidized, we need to consider the oxidation potentials of the ions. The higher the oxidation potential, the greater the ability to be oxidized.

Now, let's find the reduction and oxidation potentials for each ion and arrange them accordingly.

Reduction Potentials (in V):
Cu2+: +0.34 V
Zn2+: -0.76 V
Mg2+: -2.37 V
Al3+: -1.66 V

Oxidation Potentials (in V):
Cu2+: -0.34 V
Zn2+: +0.763 V
Mg2+: +2.37 V
Al3+: +1.66 V

Based on the reduction potentials:
Arranging the ions in decreasing order of ability to be reduced:
Mg2+ > Al3+ > Cu2+ > Zn2+

Based on the oxidation potentials:
Arranging the ions in decreasing order of ability to be oxidized:
Zn2+ > Al3+ > Cu2+ > Mg2+

Therefore, the ions arranged in order of decreasing ability to be reduced are: Mg2+ > Al3+ > Cu2+ > Zn2+.
And the ions arranged in order of decreasing ability to be oxidized are: Zn2+ > Al3+ > Cu2+ > Mg2+.