The halogen having Greenish - yellow gas reacts with hot and concentrated NaOH solution, and give products. The oxidation state of that halogen changes from 

Options

A. `0 to -1`
B. `0 to +5`
C. `-1 and + 1`
D. `0 to ''-1'' and ''+5''`

Answer

To solve the problem, we need to identify the halogen that is a greenish-yellow gas, determine the reaction it undergoes with hot and concentrated sodium hydroxide (NaOH), and analyze the changes in its oxidation state.

### Step-by-Step Solution:

1. **Identify the Halogen:**
- The halogen that is a greenish-yellow gas is chlorine (Cl2).

2. **Write the Reaction:**
- When chlorine gas reacts with hot and concentrated sodium hydroxide, the reaction can be represented as:
\[ \text{Cl}_2 + \text{NaOH} \rightarrow \text{NaClO}_3 + \text{NaCl} + \text{H}_2\text{O} \]

3. **Balance the Reaction:**
- The balanced chemical equation for the reaction is:
\[ 3\text{Cl}_2 + 6\text{NaOH} \rightarrow \text{NaClO}_3 + 5\text{NaCl} + 3\text{H}_2\text{O} \]

4. **Determine the Oxidation States:**
- In Cl2, the oxidation state of chlorine is 0 (as it is in its elemental form).
- In sodium chloride (NaCl), the oxidation state of chlorine is -1.
- In sodium chlorate (NaClO3), we need to calculate the oxidation state of chlorine. Let x be the oxidation state of chlorine:
\[ x + 3(-2) + 1 = 0 \implies x - 6 + 1 = 0 \implies x = +5 \]
- Therefore, the oxidation states of chlorine in the products are -1 in NaCl and +5 in NaClO3.

5. **Conclusion:**
- The oxidation state of chlorine changes from 0 in Cl2 to -1 in NaCl and +5 in NaClO3. Thus, the change in oxidation states is from 0 to -1 and +5.

6. **Select the Correct Option:**
- The correct option that matches this change is option 4: 0 to -1 and +5.

### Final Answer:
The oxidation state of chlorine changes from 0 to -1 and +5.

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