In the above conversion the correct sequence of reagents to be added is

The required transformations are:

- Bromination at position 2

- Conversion of $$-NO_2$$ to $$-Cl$$

- Oxidation of $$-CH_3$$ to $$-COOH$$

Bromination must be carried out first. In 4-nitrotoluene, the $$-CH_3$$ group is ortho/para-directing and the $$-NO_2$$ group is meta-directing; both direct bromination to position 2.

$$\text{4-Nitrotoluene} \xrightarrow{Br_2/Fe} \text{2-Bromo-4-nitrotoluene}$$

The nitro group is then reduced to an amino group.

$$-NO_2 \xrightarrow{Fe/H^+} -NH_2$$

The amino group is converted into a diazonium salt and subsequently replaced by chlorine via the Sandmeyer reaction.

$$-NH_2 \xrightarrow{HONO} -N_2^+Cl^- \xrightarrow{CuCl} -Cl$$

Finally, the methyl group is oxidized to a carboxylic acid.

$$-CH_3 \xrightarrow{KMnO_4} -COOH$$

Thus, the correct sequence is

$$Br_2/Fe \;\rightarrow\; Fe/H^+ \;\rightarrow\; HONO \;\rightarrow\; CuCl \;\rightarrow\; KMnO_4$$

Hence, the correct answer is

$$\boxed{\text{Option D}}$$