Step 1: Understanding the Question:
The question presents a two-step organic transformation starting with an alkyl halide (bromomethane) and asks us to identify the final product 'B'.
Step 2: Key Formula or Approach:
1. The reaction of an alkyl halide with silver nitrite ($\text{AgNO}_2$) is a nucleophilic substitution reaction where the nitrogen atom acts as the nucleophile due to the covalent nature of the Ag-O bond, primarily yielding a nitroalkane.
2. The subsequent treatment of a nitroalkane with a metal in a mineral acid (Sn / HCl) reduces the nitro group ($\text{-NO}_2$) completely to a primary amino group ($\text{-NH}_2$).
Step 3: Detailed Explanation:
3.
First Step (Formation of A): Bromomethane ($\text{CH}_3\text{Br}$) reacts with silver nitrite ($\text{AgNO}_2$). Because the bond between silver and oxygen is highly covalent, the lone pair on the nitrogen atom attacks the methyl group, leading to the formation of nitromethane ($\text{CH}_3\text{NO}_2$) as the major product 'A':
$$\text{CH}_3\text{Br} + \text{AgNO}_2 \rightarrow \text{CH}_3\text{NO}_2\text{ (A)} + \text{AgBr}$$
4.
Second Step (Formation of B): Nitromethane (A) is treated with tin and concentrated hydrochloric acid (Sn / HCl). This is a powerful reducing combination that supplies nascent hydrogen to completely reduce the nitro group into a primary amine group:
$$\text{CH}_3\text{NO}_2 \xrightarrow{\text{Sn / HCl}} \text{CH}_3\text{NH}_2\text{ (B)} + 2\text{H}_2\text{O}$$
The resulting molecule 'B' is methanamine (methylamine).
Step 4: Final Answer:
The final product 'B' is $\text{CH}_3\text{NH}_2$, which corresponds to option (B).