The term 'thio' is used in the names of all of the following compounds except :

Options

A. `Na_(2)S_(2)O_(3)`
B. `Na_(2)S_(2)O_(6)`
C. `NaSCN`
D. `Na_(2)SO_(3)`

Explanation

To solve the question regarding the use of the term 'thio' in the names of compounds, we need to analyze each of the given compounds to determine whether oxygen is replaced by sulfur in their structures. The term 'thio' is specifically used when an oxygen atom in a compound is substituted by a sulfur atom.

Let's go through each compound step by step:

### Step 1: Analyze Na2S2O3
- **Ions formed**: Na⁺ and S2O3²⁻.
- **Structure of S2O3²⁻**:
- It consists of two sulfur atoms and three oxygen atoms.
- The structure can be represented as: S=S=O, O⁻, O⁻.
- **Conclusion**: In this compound, one of the oxygen atoms can be replaced by sulfur. Therefore, 'thio' can be used for Na2S2O3.

### Step 2: Analyze Na2S2O6
- **Ions formed**: Na⁺ and S2O6²⁻.
- **Structure of S2O6²⁻**:
- It consists of two sulfur atoms and six oxygen atoms.
- The structure can be represented as: S=O, S=O, O⁻, O⁻.
- **Conclusion**: Here, oxygen is replaced by sulfur in the structure. Thus, 'thio' can be used for Na2S2O6.

### Step 3: Analyze NaSCN
- **Ions formed**: Na⁺ and SCN⁻.
- **Structure of SCN⁻**:
- It consists of sulfur, carbon, and nitrogen.
- The structure can be represented as: S-C≡N.
- **Conclusion**: In this case, sulfur is present in the compound, and it can replace an oxygen atom. Therefore, 'thio' can be used for NaSCN.

### Step 4: Analyze Na2SO3
- **Ions formed**: Na⁺ and SO3²⁻.
- **Structure of SO3²⁻**:
- It consists of one sulfur atom and three oxygen atoms.
- The structure can be represented as: S=O, O⁻, O⁻.
- **Conclusion**: In this compound, sulfur is the central atom and there are no oxygen atoms that can be replaced by sulfur. Therefore, 'thio' cannot be used for Na2SO3.

### Final Answer
The term 'thio' is used in the names of all of the following compounds except **Na2SO3**.

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