The conversion of propan-1-ol to n-butylamine involves the sequential addition of reagents. The correct sequential order of reagents is

Explanation: Propan-1-ol $$\mathrm{CH_3-CH_2-CH_2-OH}$$ contains a 3-carbon chain, while n-butylamine $$\mathrm{CH_3-CH_2-CH_2-CH_2-NH_2}$$ contains a 4-carbon chain.

Therefore, a one-carbon chain extension is required.

Step 1: Treatment with $$\mathrm{SOCl_2}$$ converts the alcohol into an alkyl chloride:

$$\mathrm{CH_3-CH_2-CH_2-OH + SOCl_2 \rightarrow CH_3-CH_2-CH_2-Cl + SO_2 + HCl}$$

This forms $$\mathrm{1\text{-}chloropropane}$$.

Step 2: Reaction with $$\mathrm{KCN}$$ gives nucleophilic substitution through an $$\mathrm{S_N2}$$ mechanism:

$$\mathrm{CH_3-CH_2-CH_2-Cl + KCN \rightarrow CH_3-CH_2-CH_2-C \equiv N + KCl}$$

This forms $$\mathrm{butanenitrile}$$.

Step 3: Reduction of the nitrile group using $$\mathrm{H_2/Ni}$$ converts it into a primary amine:

$$\mathrm{CH_3-CH_2-CH_2-C \equiv N + 4[H] \rightarrow CH_3-CH_2-CH_2-CH_2-NH_2}$$

Thus, the required sequence is $$\mathrm{(i)\ SOCl_2 \quad (ii)\ KCN \quad (iii)\ H_2/Ni}$$