Which one of the following dissolves in hot concentrated `NaOH?`

Options

A. `Fe`
B. `Zn`
C. `Cu`
D. `Ag`

Answer

To determine which metal dissolves in hot concentrated NaOH, we can follow these steps:

### Step 1: Identify the metals provided
The metals given in the question are:
- Iron (Fe)
- Zinc (Zn)
- Copper (Cu)
- Silver (Ag)

### Step 2: Understand the properties of the metals
We need to understand the reactivity of these metals with bases, specifically hot concentrated sodium hydroxide (NaOH).

### Step 3: Check for amphoteric nature
Among the metals listed, we need to identify which one is amphoteric. Amphoteric metals can react with both acids and bases.

- **Iron (Fe)**: Generally reacts with acids but does not dissolve in NaOH.
- **Zinc (Zn)**: Is amphoteric and can react with both acids and bases.
- **Copper (Cu)**: Does not react with bases.
- **Silver (Ag)**: Does not react with bases.

### Step 4: Reaction of Zinc with NaOH
Since zinc is amphoteric, we can write the reaction of zinc with hot concentrated NaOH:

\[ \text{Zn} + 2 \text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2 \uparrow \]

In this reaction, sodium zincate (Na₂ZnO₂) is formed, and hydrogen gas is evolved.

### Step 5: Conclusion
Based on the above analysis, the only metal that dissolves in hot concentrated NaOH is **Zinc (Zn)**.

### Final Answer
**Zinc (Zn)** is the metal that dissolves in hot concentrated NaOH.

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