Standard electrode potential data is given below :
`Fe^(3+) (aq) + e ^(-) rarr Fe^(2+) (aq) , E^(o) = + 0.77 V `
`Al^(3+) (aq) + 3e^(-) rarr Al (s) , E^(o) = - 1.66 V `
`Br_(2) (aq) + 2e^(-) rarr 2Br^(-) (aq) , E^(o) = +1.08 V`
Based on the data given above, reducing power of `Fe^(2+)` Al and `Br^(-)` will increase in the order :

Options

A. `Br^(-) lt Fe^(2+) ltAl `
B. `Fe^(2+) lt Al lt Br^(-)`
C. `Al lt Br ^(-) ltFe^(2+)`
D. `Al lt Fe^(2+) lt Br^(-)`

Answer

To determine the increasing order of reducing power of \( Fe^{2+} \), \( Al \), and \( Br^- \) based on the given standard electrode potentials, we can follow these steps:

### Step 1: Understand the concept of reducing power
Reducing agents are substances that can donate electrons in a chemical reaction. The stronger the reducing agent, the more readily it donates electrons. The standard reduction potential (\( E^\circ \)) indicates the tendency of a species to gain electrons (be reduced). A more negative \( E^\circ \) value corresponds to a stronger reducing agent.

### Step 2: List the standard reduction potentials
From the data provided:
- \( Fe^{3+} + e^- \rightarrow Fe^{2+} \), \( E^\circ = +0.77 \, V \)
- \( Al^{3+} + 3e^- \rightarrow Al \), \( E^\circ = -1.66 \, V \)
- \( Br_2 + 2e^- \rightarrow 2Br^- \), \( E^\circ = +1.08 \, V \)

### Step 3: Identify the reducing agents
To find the reducing power, we need to consider the oxidation reactions (reverse of the reduction reactions):
- For \( Fe^{2+} \): \( Fe^{2+} \rightarrow Fe^{3+} + e^- \) (oxidation potential = -0.77 V)
- For \( Al \): \( Al \rightarrow Al^{3+} + 3e^- \) (oxidation potential = +1.66 V)
- For \( Br^- \): \( Br^- \rightarrow Br_2 + 2e^- \) (oxidation potential = -1.08 V)

### Step 4: Compare the oxidation potentials
The more positive the oxidation potential, the stronger the reducing agent:
- \( Fe^{2+} \): \( -0.77 \, V \)
- \( Al \): \( +1.66 \, V \)
- \( Br^- \): \( -1.08 \, V \)

### Step 5: Determine the order of reducing power
From the oxidation potentials:
- \( Al \) has the highest oxidation potential, thus it is the strongest reducing agent.
- \( Fe^{2+} \) has a lower oxidation potential than \( Br^- \).
- \( Br^- \) has the lowest oxidation potential, making it the weakest reducing agent.

### Final Order
Thus, the increasing order of reducing power is:
\[ Br^- < Fe^{2+} < Al \]