Correct Answer – B
In reaction (1), aluminim is oxidizes because oxygen is added to it while ferrous ferric oxide `(Fe_3O_4)` is reduced because oxygen has been removed from it. In reaction (3), chlorine isn reuced due to the addition of hydrogen to it whilen ` H_2S` is oxidized due to the removal of hydrogen from S or we can say due to the addition of chlorine (an electronegative element ) to hydrogen. In reaction (2) , the classical concept of redox reactions fails necause both Na and `H_2` are of similar nature, i.e., both are electropositive elements (possessing the tendency to form positive ions ). Accoring to the classical concept , Na is reduced to `NaH` due to the addition fo hydency to it and `H_2` is also reduced due to the addition fo electropositive element to it, However, with the caraful application of the concept of electronegativity, we conclude that Na is oxidized while hydrogen is reduced. Thus, reaction (3) prompts us to think in terms of another way to define redox reactions. We face similar problem in the following reaction:
`Cl_(2)+3F_(2) rarr 2ClF_(3)`
as both `Cl_(2)` and `F_(2)` are electronegative elements.