Identify the total number of atoms in product Q in the given sequence of reaction `C_(6)H_(5)NH_(2)overset(NaNO_(2)+HCl)rarr Xoverset(Cu_(2)(CN)_(2))rarr Yoverset(H_(2)O //H^(+))rarrZoverset(NaOH//CaO,Delta)rarrPoverset(Cl_(2)hv"(Excess)")rarrQ`

Answer

To solve the question of identifying the total number of atoms in product Q from the given sequence of reactions, we will break down each step of the reaction sequence.

### Step-by-Step Solution:

1. **Identify the Starting Compound (Aniline)**:
The starting compound is aniline, which has the molecular formula \( C_6H_5NH_2 \).

2. **First Reaction (Formation of Benzene-Diazonium Chloride)**:
Aniline reacts with sodium nitrite (\( NaNO_2 \)) and hydrochloric acid (\( HCl \)) to form benzene-diazonium chloride (\( C_6H_5N_2Cl \)).
- **Atoms Count**:
- Carbon (C): 6
- Hydrogen (H): 5
- Nitrogen (N): 2
- Chlorine (Cl): 1
- **Total Atoms in X**: \( 6 + 5 + 2 + 1 = 14 \)

3. **Second Reaction (Formation of Cyanobenzene)**:
Benzene-diazonium chloride reacts with cuprous cyanide (\( Cu_2(CN)_2 \)) to form cyanobenzene (benzonitrile, \( C_6H_5CN \)).
- **Atoms Count**:
- Carbon (C): 6
- Hydrogen (H): 5
- Nitrogen (N): 1
- **Total Atoms in Y**: \( 6 + 5 + 1 = 12 \)

4. **Third Reaction (Hydrolysis to Benzoic Acid)**:
Cyanobenzene undergoes hydrolysis to form benzoic acid (\( C_6H_5COOH \)).
- **Atoms Count**:
- Carbon (C): 7 (6 from the benzene part + 1 from the carboxylic acid)
- Hydrogen (H): 6 (5 from the benzene part + 1 from the carboxylic acid)
- Oxygen (O): 2
- **Total Atoms in Z**: \( 7 + 6 + 2 = 15 \)

5. **Fourth Reaction (Decarboxylation to Benzene)**:
Benzoic acid reacts with sodium hydroxide and heat (soda lime) to produce benzene (\( C_6H_6 \)).
- **Atoms Count**:
- Carbon (C): 6
- Hydrogen (H): 6
- **Total Atoms in P**: \( 6 + 6 = 12 \)

6. **Fifth Reaction (Chlorination of Benzene)**:
Benzene is treated with chlorine (\( Cl_2 \)) in the presence of light (excess chlorine) to form benzene hexachloride (\( C_6H_6Cl_6 \)).
- **Atoms Count**:
- Carbon (C): 6
- Hydrogen (H): 6
- Chlorine (Cl): 6
- **Total Atoms in Q**: \( 6 + 6 + 6 = 18 \)

### Final Answer:
The total number of atoms in product Q is **18**.