1. Identify what is needed

We need a reagent that will reduce $Fe^{3+}$ to $Fe^{2+}$.

That means the reagent itself must act as a reducing agent.

$Fe^{3+} + e^- \rightarrow Fe^{2+}$

So we must check in which medium the given peroxide species behave as reducing agents.

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2. Key redox behavior of peroxides

(i) $H_2O_2$

Hydrogen peroxide can act as both:

• oxidizing agent
• reducing agent

Its behavior depends on the medium and the reacting species.

A very important reaction is:

$2Fe^{3+} + H_2O_2 \rightarrow 2Fe^{2+} + O_2 + 2H^+$

Here, $H_2O_2$ is oxidized to $O_2$, so it acts as a reducing agent. Thus it can reduce $Fe^{3+}$ to $Fe^{2+}$.

This is feasible in acidic medium.

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(ii) In alkaline medium

In presence of $NaOH$, $H_2O_2$ generally shows strong oxidizing behavior because of formation of peroxide/hydroperoxide species in base. It is not the standard reagent used for reducing $Fe^{3+}$ to $Fe^{2+}$.

So option A is not correct.

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3. Check each option

Option A: $H_2O_2$ in presence of $NaOH$

In alkaline medium, $H_2O_2$ is not used here as a reducing agent for $Fe^{3+}$.

So, A is incorrect.

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Option B: $Na_2O_2$ in water

$Na_2O_2$ in water gives hydrogen peroxide:

$Na_2O_2 + 2H_2O \rightarrow 2NaOH + H_2O_2$

This produces alkaline medium along with $H_2O_2$. Since the medium becomes basic, this does not favor reduction of $Fe^{3+}$ to $Fe^{2+}$.

So, B is incorrect.

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Option C: $H_2O_2$ in presence of $H_2SO_4$

This is acidic medium. In acidic medium, $H_2O_2$ can reduce $Fe^{3+}$ to $Fe^{2+}$:

$2Fe^{3+} + H_2O_2 \rightarrow 2Fe^{2+} + O_2 + 2H^+$

So, C is correct.

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Option D: $Na_2O_2$ in presence of $H_2SO_4$

First, $Na_2O_2$ with acid generates $H_2O_2$:

$Na_2O_2 + H_2SO_4 \rightarrow Na_2SO_4 + H_2O_2$

Since the medium is acidic, the generated $H_2O_2$ can reduce $Fe^{3+}$ to $Fe^{2+}$.

So, D is correct.

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4. Final conclusion

The reagents that reduce $Fe^{3+}$ to $Fe^{2+}$ are:

$\boxed{C, D}$

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5. Comparison with stored correct answer

Stored correct answer: A, B

Derived answer: C, D

These do not match. The stored answer appears incorrect because reduction of $Fe^{3+}$ by peroxide is favored in acidic medium, not in alkaline medium.