Complete the following reaction,
`Na_2B_4O_7 + 7H_2O ` `rarr` 2NaOH+….`
Choose the correct option.

Options

A. `underset("Orthoboric acid")(4H_3BO_3)`
B. `underset("Boric acid")(4H_3BO_3)`
C. `underset("Orthoboric acid")(2H_3BO_3)`
D. `underset("Boric acid")(2H_3BO_3)`

Answer

To complete the reaction given in the question, we will follow these steps:

### Step 1: Write the initial reaction
We start with the given reactants:
\[ \text{Na}_2\text{B}_4\text{O}_7 + 7\text{H}_2\text{O} \]

### Step 2: Identify the products
When sodium tetraborate (\(\text{Na}_2\text{B}_4\text{O}_7\)) reacts with water, it produces sodium hydroxide (\(\text{NaOH}\)) and orthoboric acid (\(\text{H}_3\text{BO}_3\)).

### Step 3: Write the unbalanced equation
The unbalanced equation can be written as:
\[ \text{Na}_2\text{B}_4\text{O}_7 + 7\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_3\text{BO}_3 \]

### Step 4: Balance the equation
Now, we need to balance the products. We have 4 boron atoms in \(\text{Na}_2\text{B}_4\text{O}_7\), so we will need 4 molecules of \(\text{H}_3\text{BO}_3\) to balance the boron:
\[ \text{Na}_2\text{B}_4\text{O}_7 + 7\text{H}_2\text{O} \rightarrow 2\text{NaOH} + 4\text{H}_3\text{BO}_3 \]

### Step 5: Check the balance
Now, let's check if the equation is balanced:
- **Sodium (Na)**: 2 on both sides
- **Boron (B)**: 4 on both sides (from 4 \(\text{H}_3\text{BO}_3\))
- **Oxygen (O)**: Left side has \(7 + 7 = 14\) (from 7 \(\text{H}_2\text{O}\) and 4 from \(\text{Na}_2\text{B}_4\text{O}_7\)), right side has \(2 + 12 = 14\) (2 from \(\text{NaOH}\) and 12 from 4 \(\text{H}_3\text{BO}_3\))
- **Hydrogen (H)**: Left side has \(14\) (from \(7 \text{H}_2\text{O}\)), right side has \(2 + 12 = 14\) (2 from \(\text{NaOH}\) and 12 from 4 \(\text{H}_3\text{BO}_3\))

Since all elements are balanced, the final balanced equation is:
\[ \text{Na}_2\text{B}_4\text{O}_7 + 7\text{H}_2\text{O} \rightarrow 2\text{NaOH} + 4\text{H}_3\text{BO}_3 \]

### Final Answer
The correct completion of the reaction is:
\[ 4\text{H}_3\text{BO}_3 \]