The standard reduction potential at 298 K for the following half reactions are given below:
`Fe^(3+)(1M)+e^(-)rarrFe^(2+)(aq),E^(o)=0.770 V,`
`Zn^(2+)(1M)+2e^(-)rarrZn(s),E^(o)=-0.762 V`
`Cd^(2+)(1M)+2e^(-)rarrCd(s),E^(o)=-0.402 V,`
`2H^(+)(1M)+2e^(-)rarrH_(2)(g),E^(o) = 0.00 V.`
The strpongest reducing agent is:

Options

A. Zn(s)
B. Cd(s)
C. `H_(2)(g)`
D. `Fe^(2+)(aq)`

Answer

To determine the strongest reducing agent from the given half-reactions and their standard reduction potentials, we can follow these steps:

### Step 1: Understand the concept of reducing agents
A reducing agent is a substance that donates electrons to another substance, causing the other substance to be reduced. In the process, the reducing agent itself gets oxidized. The strength of a reducing agent is inversely related to its standard reduction potential (E°). A lower (more negative) reduction potential indicates a greater tendency to be oxidized, thus acting as a stronger reducing agent.

### Step 2: List the given half-reactions and their standard reduction potentials
1. \( Fe^{3+} + e^- \rightarrow Fe^{2+}, \quad E^\circ = 0.770 \, V \)
2. \( Zn^{2+} + 2e^- \rightarrow Zn(s), \quad E^\circ = -0.762 \, V \)
3. \( Cd^{2+} + 2e^- \rightarrow Cd(s), \quad E^\circ = -0.402 \, V \)
4. \( 2H^+ + 2e^- \rightarrow H_2(g), \quad E^\circ = 0.00 \, V \)

### Step 3: Identify the reducing agents from the given half-reactions
To find the strongest reducing agent, we need to look for the species that has the lowest standard reduction potential among the given half-reactions. The lower the E° value, the stronger the reducing agent.

### Step 4: Compare the standard reduction potentials
- \( E^\circ \) for \( Fe^{3+} \) is \( 0.770 \, V \) (not a strong reducing agent)
- \( E^\circ \) for \( Zn^{2+} \) is \( -0.762 \, V \) (potentially a strong reducing agent)
- \( E^\circ \) for \( Cd^{2+} \) is \( -0.402 \, V \) (not as strong as Zn)
- \( E^\circ \) for \( H^+ \) is \( 0.00 \, V \) (not a strong reducing agent)

### Step 5: Identify the strongest reducing agent
Among the given half-reactions, \( Zn^{2+} \) has the lowest standard reduction potential of \( -0.762 \, V \). This indicates that zinc has the greatest tendency to be oxidized, making it the strongest reducing agent.

### Conclusion
The strongest reducing agent among the options provided is **Zinc (Zn)**.

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