A metal is burnt in air and the ash on moistening smells of ammonia. The metal is

Options

A. `Na`
B. `Fe`
C. `Mg`
D. `Al`

Answer

To determine the metal that, when burnt in air, produces ash that smells of ammonia upon moistening, we can follow these steps:

### Step 1: Identify the properties of the metal
The metal must be capable of forming a nitride when burnt in air. This nitride, when moistened, should release ammonia gas.

**Hint:** Look for metals known to form nitrides.

### Step 2: Consider the group of metals
Among the s-block elements, lithium and magnesium are known to form nitrides. Lithium forms lithium nitride (Li3N), while magnesium forms magnesium nitride (Mg3N2).

**Hint:** Recall the diagonal relationship of elements in the periodic table.

### Step 3: Analyze the formation of nitrides
When magnesium is burnt in air, it forms magnesium nitride (Mg3N2). This is crucial because we need to find out what happens when this nitride interacts with moisture.

**Hint:** Think about the reaction of nitrides with water.

### Step 4: Reaction with water
When magnesium nitride (Mg3N2) reacts with water, it produces magnesium hydroxide (Mg(OH)2) and ammonia (NH3):

\[ \text{Mg}_3\text{N}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Mg(OH)}_2 + 2\text{NH}_3 \]

This reaction confirms that ammonia is released when the ash is moistened.

**Hint:** Write down the balanced chemical equation to visualize the products.

### Step 5: Conclusion
Based on the analysis, the metal that, when burnt in air, produces ash that smells of ammonia upon moistening is magnesium.

**Final Answer:** The metal is magnesium.

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