`A overset(Delta)rarrB` (oxide) `+ CO_(2)`
`B + H_(2)O rarr C`
`C+ CO_(2) rarrA` (milky)
`C+ NH_(4)CI overset(Delta)rarr D` (gas)
`D + H_(2)O + CO_(2) rarr E`
`E + NaCI rarr F`
`F overset(Delta)rarr Na_(2)CO_(3)+CO_(2)+H_(2)O`
B and C are:

Options

A. `CaO, Ca(OH)_(2)`
B. `Ca(OH)_(2), CaCO_(3)`
C. `CaCO_(3), Ca(OH)_(2)`
D. `Ca(OH)_(2), CaO`

Answer

To solve the problem, we will analyze the given reactions step by step and identify the compounds B and C based on the information provided.

### Step-by-Step Solution:

1. **Identify Compound A**:
- The first reaction is \( A \overset{\Delta}{\rightarrow} B + CO_2 \).
- Since the product B is an oxide and the reaction produces carbon dioxide, we can assume that A is calcium carbonate (CaCO3), which decomposes upon heating to form calcium oxide (CaO) and carbon dioxide (CO2).
- Therefore, **A = CaCO3**.

2. **Identify Compound B**:
- From the decomposition of A, we have \( CaCO3 \overset{\Delta}{\rightarrow} CaO + CO_2 \).
- Thus, **B = CaO** (calcium oxide).

3. **Identify Compound C**:
- The next reaction is \( B + H_2O \rightarrow C \).
- When calcium oxide (B) reacts with water, it forms calcium hydroxide (Ca(OH)2).
- Therefore, **C = Ca(OH)2** (calcium hydroxide).

4. **Verify the Next Reactions**:
- The next reaction is \( C + CO_2 \rightarrow A \).
- Calcium hydroxide (C) reacts with carbon dioxide to form calcium carbonate (A), confirming our earlier identification.
- This is consistent with the equation: \( Ca(OH)2 + CO_2 \rightarrow CaCO3 + H2O \).

5. **Continue with the Remaining Reactions**:
- The reaction \( C + NH_4Cl \overset{\Delta}{\rightarrow} D \) indicates that calcium hydroxide reacts with ammonium chloride to produce ammonia gas (D).
- The reaction can be represented as: \( Ca(OH)2 + 2NH4Cl \rightarrow CaCl2 + 2NH3 + 2H2O \).
- Thus, **D = NH3** (ammonia gas).

6. **Further Reactions**:
- The next reaction \( D + H_2O + CO_2 \rightarrow E \) indicates that ammonia gas reacts with water and carbon dioxide to form ammonium bicarbonate (E).
- Therefore, **E = NH4HCO3** (ammonium bicarbonate).

7. **Final Reactions**:
- The reaction \( E + NaCl \rightarrow F \) indicates that ammonium bicarbonate reacts with sodium chloride to form sodium bicarbonate (F).
- Thus, **F = NaHCO3** (sodium bicarbonate).
- The final reaction \( F \overset{\Delta}{\rightarrow} Na2CO3 + CO2 + H2O \) confirms that sodium bicarbonate decomposes upon heating to form sodium carbonate, carbon dioxide, and water.

### Conclusion:
- After analyzing all the reactions, we conclude that:
- **B = CaO** (calcium oxide)
- **C = Ca(OH)2** (calcium hydroxide)