The native silver forms a water soluble compound (B) with dilute aqueous solution of NaCN in the presence of a gas (A). The silver metal is obtained by the addition of a metal (C) to (B) and complex (D) is formed as a byproduct. Write the structures of (C) and (D) and identify (A) and (B) in the following sequence :
`Ag+NaCN+[A] +H_(2)O [B]+OH^(-) +Na^(+) [C] +[B] [D]+Ag`

Answer

To solve the problem, we need to identify the compounds and gases involved in the reaction sequence provided. Let's break down the information step by step.

### Step 1: Identify Gas (A)
The question mentions that native silver reacts with a dilute aqueous solution of NaCN in the presence of a gas (A). In this context, the gas that facilitates the formation of a soluble silver compound is **oxygen (O₂)**.

**Hint:** Think about gases that are commonly involved in oxidation reactions with metals.

### Step 2: Identify Compound (B)
The soluble compound formed when native silver reacts with NaCN in the presence of oxygen is **sodium argentocyanide**, which can be represented as **Na[Ag(CN)₂]**. This complex is formed through the reaction of silver with cyanide ions in the presence of oxygen.

**Hint:** Look for a complex ion that contains silver and cyanide ions.

### Step 3: Identify Metal (C)
The question states that silver metal is obtained by adding a metal (C) to the compound (B). A common metal used to reduce silver ions back to metallic silver is **zinc (Zn)**.

**Hint:** Consider metals that are known to reduce silver ions in solution.

### Step 4: Identify Complex (D)
When zinc is added to the sodium argentocyanide solution, it reduces the silver ions to metallic silver and forms a complex as a byproduct. The complex formed is **sodium zinc cyanide**, represented as **Na₂[Zn(CN)₄]**.

**Hint:** Look for a complex that includes zinc and cyanide ions.

### Summary of Identifications
- **Gas (A)**: Oxygen (O₂)
- **Compound (B)**: Sodium argentocyanide, Na[Ag(CN)₂]
- **Metal (C)**: Zinc (Zn)
- **Complex (D)**: Sodium zinc cyanide, Na₂[Zn(CN)₄]

### Final Structures
- **Structure of (C)**: Zinc (Zn)
- **Structure of (D)**: Na₂[Zn(CN)₄]

### Final Answer
- (A) = O₂
- (B) = Na[Ag(CN)₂]
- (C) = Zn
- (D) = Na₂[Zn(CN)₄]