When $Br_{2}$ is added to $CH_{2}=CH_{2}$ in presence of NaCl the product of the reaction is:

Question

Accepted Answer

When $Br_{2}$ is added to $CH_{2}=CH_{2}$ in the presence of NaCl, the reaction involves the addition of halogens across the double bond of ethylene ($CH_{2}=CH_{2}$). The presence of NaCl introduces chloride ions into the reaction mixture, which can participate in the reaction mechanism.

1. **Explanation for Option 3 being correct:**

The reaction proceeds through the formation of a bromonium ion intermediate when $Br_{2}$ is added to the double bond. This intermediate is a three-membered ring structure where one of the bromine atoms is temporarily bonded to both carbon atoms of the former double bond. The bromonium ion is positively charged and highly reactive, making it susceptible to nucleophilic attack.

In the presence of NaCl, chloride ions (Cl⁻) are available as nucleophiles. These chloride ions can attack the bromonium ion, leading to the formation of a product where one carbon is bonded to a bromine atom and the other to a chlorine atom, resulting in $CH_2(Cl)-CH_2(Br)$. Additionally, bromide ions (Br⁻) are also present in the reaction mixture, which can similarly attack the bromonium ion, leading to the formation of $CH_2(Br)-CH_2(Br)$.

Therefore, both $CH_2(Br)-CH_2(Br)$ and $CH_2(Cl)-CH_2(Br)$ are formed as products, justifying why Option 3, "Both (1) and (2)," is the correct answer.

2. **Explanation for why each of the other options is incorrect:**

- **Option 1: $CH_2(Br)-CH_2(Br)$** is incorrect as the sole product because it does not account for the presence of chloride ions from NaCl, which can also participate in the reaction to form $CH_2(Cl)-CH_2(Br)$.

- **Option 2: $CH_2(Cl)-CH_2(Br)$** is incorrect as the sole product because it does not account for the bromide ions that are also present and capable of forming $CH_2(Br)-CH_2(Br)$.

- **Option 4: $CH_2(Cl)-CH_2(Cl)$** is incorrect because the reaction primarily involves $Br_{2}$, and the formation of a dibromo product is expected. The presence of chloride ions allows for the formation of mixed halogen products, but not exclusively dichloro products.

In conclusion, the presence of both bromide and chloride ions in the reaction mixture leads to the formation of both $CH_2(Br)-CH_2(Br)$ and $CH_2(Cl)-CH_2(Br)$, making Option 3 the correct answer.