1. Target transformation

We need to convert nitrobenzene to m-dibromobenzene.

Nitrobenzene already has one substituent: $-\mathrm{NO_2}$. The nitro group is:

• strongly deactivating
• meta-directing

So if we brominate nitrobenzene first, bromine will enter the meta position, giving m-bromonitrobenzene. After that, if we convert the $-\mathrm{NO_2}$ group into $-\mathrm{Br}$, we will obtain 1,3-dibromobenzene (m-dibromobenzene).

So the logical sequence is:

This is the Sandmeyer route.

2. Check each option

Option A

$\mathrm{NaNO_2} / \mathrm{HCl} / \mathrm{KBr} / \mathrm{H^+}$

This starts directly with diazotization reagents. But nitrobenzene is not an amine, so it cannot be diazotized directly.

So A is incorrect.

Option B

$\mathrm{Sn/HCl} / \mathrm{KBr} / \mathrm{Br_2} / \mathrm{H^+}$

• $\mathrm{Sn/HCl}$ reduces nitrobenzene to aniline.
• Then $\mathrm{KBr}$ alone does nothing useful here.
• Also, bromination of aniline is not suitable for obtaining the required meta product; aniline is ortho/para directing and highly activating.

So B is incorrect.

Option C

$\mathrm{Br_2/Fe} / \mathrm{Sn/HCl} / \mathrm{NaNO_2/HCl} / \mathrm{CuBr/HBr}$

Stepwise:

1. Bromination $\mathrm{C_6H_5NO_2} \xrightarrow{\mathrm{Br_2/Fe}} m\text{-bromonitrobenzene}$ because $-\mathrm{NO_2}$ is meta-directing.

2. Reduction of nitro group $m\text{-bromonitrobenzene} \xrightarrow{\mathrm{Sn/HCl}} m\text{-bromoaniline}$

3. Diazotization $m\text{-bromoaniline} \xrightarrow{\mathrm{NaNO_2/HCl}} m\text{-bromobenzenediazonium chloride}$

4. Sandmeyer reaction $m\text{-bromobenzenediazonium chloride} \xrightarrow{\mathrm{CuBr/HBr}} m\text{-dibromobenzene}$

This gives the desired product.

So C is correct.

Option D

$\mathrm{Sn/HCl} / \mathrm{Br_2} / \mathrm{NaNO_2} / \mathrm{NaBr}$

• $\mathrm{Sn/HCl}$ converts nitrobenzene to aniline.
• Bromination of aniline gives mainly 2,4,6-tribromoaniline, not the desired meta-bromo derivative.
• Also, diazotization requires acidic medium, and $\mathrm{NaBr}$ alone is not the proper Sandmeyer reagent.

So D is incorrect.

3. Final answer

The correct reagent sequence is:

Hence, the correct option is C.