If the standard potential of an ion is greater than zero, then the reduced form is more stable compared to hydrogen gas. On the other hand, if the standard potential is lesser than zero, then hydrogen gas is more stable than reduced form. The positive value of the standard electrode potential means that the ions of the element can oxidise hydrogen, or hydrogen ions can reduce the atoms. The negative value of the standard electrode potential indicates that hydrogen gas can oxidise the ion, or the atom can reduce hydrogen ions. So, below the value of zero, the more negative the value of the standard electrode potential, the stronger the hydrogen gas can oxidise the ion, and the stronger the ion can be as a reducing agent. Standard electrode potential of Cr is -0.74V, which is a negative value and lower than the other mentioned values, hence it is the strongest reducing agent. The correct option is (ii).
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