Answer: Al3+ < Zn2+ < Fe2+ < Ag+
Explanation: Oxidizing Agents can be defined as those agents which oxidized the other species by getting itself reduced.
Standard Reduction potential is the tendency of the chemical species to get reduced and is also used to determine which is better oxidizing or a reducing agent.
The E°red of the following -
[tex]Al^{3+}[/tex] = -1.66V
[tex]Fe^{2+}[/tex] = -.45V
[tex]zn^{2+}[/tex] = -.76
[tex]Ag^{+}[/tex] = +.80
Thus [tex]Ag^{+}[/tex] is the best oxidizing agent among the given.