Which of the following compound is responsible for tarnishing of silver ?

Question

Accepted Answer

The compound responsible for the tarnishing of silver is Ag_2S, which is Option 3. Here is a detailed explanation supporting this:

1. **Explanation for Option 3 (Ag_2S):**
   - Silver tarnishing is primarily due to the formation of silver sulfide (Ag_2S) on the surface of silver items. This occurs when silver reacts with hydrogen sulfide (H_2S) present in the air, which can come from various sources such as pollution, volcanic activity, or even certain foods. The chemical reaction is as follows:
     $$
     2Ag + H_2S \rightarrow Ag_2S + H_2
     $$
   - The formation of Ag_2S results in a black or dark gray layer on the silver, which is commonly referred to as tarnish. This is a well-documented and widely accepted explanation for the tarnishing process.

2. **Explanation for why other options are incorrect:**

- **Option 1 (Ag_2O):**
     - Silver oxide (Ag_2O) is not responsible for tarnishing. While silver can react with oxygen to form silver oxide, this reaction is not significant under normal atmospheric conditions. Silver oxide does not form the characteristic black tarnish seen on silver items.

- **Option 2 (Ag_2CO_3):**
     - Silver carbonate (Ag_2CO_3) is not involved in the tarnishing process. It is a compound that can form under specific conditions, but it does not contribute to the typical tarnish seen on silver. Silver carbonate is not stable in the presence of moisture and carbon dioxide, and it does not produce the black layer associated with tarnish.

- **Option 4 (AgCN):**
     - Silver cyanide (AgCN) is not related to the tarnishing of silver. It is a compound that forms under very specific chemical conditions, typically involving cyanide ions. It does not occur naturally in the environment and is not responsible for the tarnishing process.

In conclusion, the tarnishing of silver is specifically due to the formation of silver sulfide (Ag_2S), making Option 3 the correct answer. The other options do not contribute to the tarnishing process and are therefore incorrect in this context.