In the manufacture of sodium carbonate, following reactions are involved:
`(A) overset(Delta)rarr (B) + CO_(2)`
`(B) +H_(2)O rarr (C ) overset(+NH_(4)Cl rarr (D)overset(+H_(2)O)rarr underset("Solution")(E )`
`(E )+CO_(2)rarr (F)`
`(F)+NaCl rarr (G) overset("Heat")rarr Na_(2)CO_(3)+CO_(2)+H_(2)O`
(D) is a gas which is soluble in `H_(2)O`
(B) is

Options

A. `CaO`
B. `Ca_(2)O_(2)`
C. `CaO_(2)`
D. `Na_(2)O`

Explanation

To solve the problem regarding the manufacture of sodium carbonate and identify what substance (B) is, we will analyze the given reactions step by step:

### Step-by-Step Solution:

1. **Identify Reaction (A)**: The first reaction is given as:
\[ (A) \overset{\Delta}{\rightarrow} (B) + CO_2 \]
This indicates that substance (A) is decomposing to form substance (B) and carbon dioxide (CO₂). In the context of sodium carbonate production, (A) is likely calcium carbonate (CaCO₃).

**Hint**: Look for a common starting material in the production of sodium carbonate.

2. **Determine (B)**: From the decomposition of calcium carbonate (CaCO₃) upon heating, we have:
\[ CaCO_3 \overset{\Delta}{\rightarrow} CaO + CO_2 \]
Therefore, (B) is calcium oxide (CaO).

**Hint**: Consider what products are formed when calcium carbonate is heated.

3. **Identify Reaction (B)**: The next reaction is:
\[ (B) + H_2O \rightarrow (C) \]
Here, calcium oxide (CaO) reacts with water (H₂O) to form calcium hydroxide (Ca(OH)₂), which is (C).

**Hint**: Think about the reaction of a metal oxide with water.

4. **Identify Reaction (C)**: The next step involves:
\[ (C) \overset{(+NH_4Cl)}{\rightarrow} (D) \]
Calcium hydroxide reacts with ammonium chloride (NH₄Cl) to produce ammonia (NH₃) and calcium chloride (CaCl₂). The gas produced here is (D), which is ammonia (NH₃).

**Hint**: Identify the gas produced when a base reacts with an ammonium salt.

5. **Identify Reaction (D)**: The gas (D) is soluble in water, confirming that (D) is indeed ammonia (NH₃).

**Hint**: Recall the properties of ammonia regarding its solubility in water.

6. **Identify Reaction (E)**: The next reaction is:
\[ (D) + H_2O \rightarrow (E) \]
Ammonia (NH₃) dissolved in water forms ammonium hydroxide (NH₄OH), which is (E).

**Hint**: Consider the behavior of ammonia when it interacts with water.

7. **Identify Reaction (F)**: The reaction involving (E) is:
\[ (E) + CO_2 \rightarrow (F) \]
Ammonium hydroxide reacts with carbon dioxide to form ammonium bicarbonate (NH₄HCO₃), which is (F).

**Hint**: Think about the reaction between a base and an acid (in this case, CO₂ acts as an acid).

8. **Identify Reaction (G)**: The final reaction is:
\[ (F) + NaCl \rightarrow (G) \overset{\text{Heat}}{\rightarrow} Na_2CO_3 + CO_2 + H_2O \]
Ammonium bicarbonate reacts with sodium chloride (NaCl) to produce sodium bicarbonate (NaHCO₃) and ammonium chloride (NH₄Cl). Upon heating, sodium bicarbonate decomposes to form sodium carbonate (Na₂CO₃), carbon dioxide, and water.

**Hint**: Consider the final products formed when sodium bicarbonate is heated.

### Final Answer:
Thus, the substance (B) in the reactions is **Calcium Oxide (CaO)**.