A metal `M` reacts with `N_(2)` to give a compound `'A'(M_(3)N)`. 'A' on heating at high temperature gives back `'M'` and `'A'` on reacting with `H_(2)O` gives a gas 'B'.'B' turns `CuSO_(4)` solution blue on passing through it `A` and `B` can be

Options

A. (a) `Li and NH_(3)`
B. (b) `Na and NH_(3)`
C. (c) `Ba and N_(2)`
D. (d) `Al and N_(2)`

Answer

To solve the problem step by step, we will analyze the information given and derive the required compounds and gases.

### Step 1: Identify the compound A
The question states that a metal \( M \) reacts with \( N_2 \) to form a compound \( A \) with the formula \( M_3N \). This indicates that \( A \) is a metal nitride.

### Step 2: Determine the possible metals
The metal \( M \) must be one that can form a nitride of the form \( M_3N \). Common metals that form nitrides include lithium, sodium, barium, and aluminum.

- **Lithium (Li)**: Can form \( Li_3N \)
- **Sodium (Na)**: Does not typically form \( Na_3N \)
- **Barium (Ba)**: Does not typically form \( Ba_3N \)
- **Aluminum (Al)**: Can form \( AlN \) but not \( Al_3N \)

From this analysis, the only viable candidate for \( M \) is **Lithium**.

### Step 3: Write the reaction for the formation of compound A
The reaction of lithium with nitrogen can be written as:
\[ 6Li + N_2 \rightarrow 2Li_3N \]
Thus, the compound \( A \) is **Lithium Nitride (\( Li_3N \))**.

### Step 4: Analyze the heating of compound A
The problem states that when compound \( A \) is heated, it gives back the metal \( M \). This indicates the decomposition of lithium nitride:
\[ 2Li_3N \rightarrow 6Li + N_2 \]
This confirms that heating \( A \) regenerates lithium.

### Step 5: Reaction of compound A with water
Next, we need to consider the reaction of \( A \) (lithium nitride) with water:
\[ Li_3N + 3H_2O \rightarrow 3LiOH + NH_3 \]
This reaction produces lithium hydroxide and ammonia gas \( (NH_3) \). Thus, the gas \( B \) is **Ammonia (\( NH_3 \))**.

### Step 6: Identify the properties of gas B
The problem states that gas \( B \) (ammonia) turns \( CuSO_4 \) solution blue. This is due to the formation of a complex between ammonia and copper ions:
\[ Cu^{2+} + 4NH_3 \rightarrow [Cu(NH_3)_4]^{2+} \]
This complex is blue in color, confirming that gas \( B \) is indeed ammonia.

### Conclusion
From the analysis, we conclude:
- The metal \( M \) is **Lithium (Li)**.
- The gas \( B \) produced is **Ammonia (NH_3)**.

Thus, the final answer is:
- \( A \) is Lithium Nitride (\( Li_3N \))
- \( B \) is Ammonia (\( NH_3 \))