Amorphous boron is extracted from borax by the following steps :
`"Borax" overset((A))rarr H_(3) BO_(3) overset("Heat")rarr B_(2) O_(3) overset((B)) rarr "Boron" (A) and (B) are`
(a) `H_(2) SO_(4), Al`
(b) `HCl`, Carbon
( c) `H_(2) SO_(4), Mg`
(d) `HCl, Fe`.

Options

A. `H_(2)SO_(4),Al`
B. `HCl`,carbon
C. `H_(2)SO_(4),Mg`
D. `HCl,Fe`

Explanation

To solve the question regarding the extraction of amorphous boron from borax, we will break down the process step by step.

### Step 1: Understand the Starting Material
- **Borax** is a compound with the formula \( \text{Na}_2\text{B}_4\text{O}_7 \). It is the starting material for the extraction of boron.

### Step 2: Identify the First Reaction
- The first step involves the reaction of borax with an acid to form boric acid.
- When borax is treated with concentrated sulfuric acid (\( \text{H}_2\text{SO}_4 \)), it produces boric acid (\( \text{H}_3\text{BO}_3 \)) and sodium sulfate (\( \text{Na}_2\text{SO}_4 \)).
- The balanced reaction can be represented as:
\[ \text{Na}_2\text{B}_4\text{O}_7 + 5 \text{H}_2\text{SO}_4 + 5 \text{H}_2\text{O} \rightarrow \text{Na}_2\text{SO}_4 + 4 \text{H}_3\text{BO}_3 \]
- Thus, **A** in the reaction is \( \text{H}_2\text{SO}_4 \).

### Step 3: Identify the Second Reaction
- The second step involves heating boric acid to produce boron oxide (\( \text{B}_2\text{O}_3 \)).
- When boric acid is heated, it loses water and forms boron oxide:
\[ 2 \text{H}_3\text{BO}_3 \xrightarrow{\text{Heat}} \text{B}_2\text{O}_3 + 3 \text{H}_2\text{O} \]

### Step 4: Identify the Final Reaction
- The final step involves reducing boron oxide (\( \text{B}_2\text{O}_3 \)) to obtain boron.
- This reduction can be achieved using magnesium (\( \text{Mg} \)), which is a strong reducing agent:
\[ \text{B}_2\text{O}_3 + 3 \text{Mg} \rightarrow 2 \text{B} + 3 \text{MgO} \]
- Thus, **B** in the reaction is \( \text{Mg} \).

### Conclusion
- Therefore, the correct answer for the unknowns A and B is:
- (A) \( \text{H}_2\text{SO}_4 \)
- (B) \( \text{Mg} \)

The correct option is (c) \( \text{H}_2\text{SO}_4, \text{Mg} \).