`Na_2 B_4 O_7 10 H_2 O overset("conc. HCl")to A.` Compound 'A' is :

Options

A. `H_2 B_4 O_7`
B. `B_2 O_3`
C. `H_3 BO_3`
D. `HBO_2`

Answer

To solve the question regarding the reaction of Na₂B₄O₇·10H₂O with concentrated HCl and to identify compound 'A', we will follow these steps:

### Step 1: Identify the Reactants
The reactant given is Na₂B₄O₇·10H₂O, which is commonly known as borax. It contains sodium (Na), boron (B), and oxygen (O) along with water of crystallization (10H₂O).

**Hint:** Look for the common name of Na₂B₄O₇·10H₂O and its components.

### Step 2: Understand the Reaction with HCl
When borax reacts with concentrated hydrochloric acid (HCl), it undergoes hydrolysis. The reaction involves the release of boric acid and sodium chloride.

**Hint:** Consider the products formed when borax reacts with an acid.

### Step 3: Write the Balanced Chemical Equation
The balanced chemical equation for the reaction can be written as follows:

\[ \text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O} + 2\text{HCl} \rightarrow 4\text{H}_3\text{BO}_3 + 2\text{NaCl} + 5\text{H}_2\text{O} \]

This indicates that 1 mole of borax reacts with 2 moles of HCl to produce 4 moles of boric acid (H₃BO₃), 2 moles of sodium chloride (NaCl), and 5 moles of water.

**Hint:** Pay attention to the stoichiometry of the reaction to identify the products.

### Step 4: Identify Compound 'A'
From the balanced equation, we see that one of the products formed is boric acid, which is represented as H₃BO₃. This is the compound 'A' that we need to identify.

**Hint:** Look for the product that is commonly known as boric acid.

### Conclusion
The compound 'A' formed from the reaction of Na₂B₄O₇·10H₂O with concentrated HCl is **H₃BO₃**, which is also known as orthoboric acid or boric acid.

**Final Answer:** Compound 'A' is **H₃BO₃** (orthoboric acid).

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