To determine which of the given salts has a pH value greater than 7, we need to analyze each salt based on the strength of the acid and base from which it is derived. A salt will have a pH greater than 7 if it is formed from a weak acid and a strong base.
### Step-by-Step Solution:
1. **Identify the salts and their components:**
- I. Sodium carbonate (Na2CO3)
- II. Sodium chloride (NaCl)
- III. Sodium sulphate (Na2SO4)
- IV. Sodium hydrogen carbonate (NaHCO3)
2. **Analyze Sodium Carbonate (Na2CO3):**
- Sodium carbonate is formed from the reaction of sodium hydroxide (NaOH, a strong base) and carbonic acid (H2CO3, a weak acid).
- Since it is derived from a strong base and a weak acid, it will be basic in nature, and thus, the pH will be greater than 7.
3. **Analyze Sodium Chloride (NaCl):**
- Sodium chloride is formed from the reaction of sodium hydroxide (NaOH, a strong base) and hydrochloric acid (HCl, a strong acid).
- Both the acid and base are strong, which means that NaCl is a neutral salt. Therefore, the pH will be around 7.
4. **Analyze Sodium Sulphate (Na2SO4):**
- Sodium sulphate is formed from the reaction of sodium hydroxide (NaOH, a strong base) and sulfuric acid (H2SO4, a strong acid).
- Again, since both components are strong, Na2SO4 is also a neutral salt, resulting in a pH around 7.
5. **Analyze Sodium Hydrogen Carbonate (NaHCO3):**
- Sodium hydrogen carbonate is formed from the reaction of sodium hydroxide (NaOH, a strong base) and carbonic acid (H2CO3, a weak acid).
- Since it is derived from a strong base and a weak acid, it will also be basic in nature, leading to a pH greater than 7.
### Conclusion:
Based on the analysis:
- Sodium carbonate (Na2CO3) and Sodium hydrogen carbonate (NaHCO3) will have a pH greater than 7.
- Sodium chloride (NaCl) and Sodium sulphate (Na2SO4) will have a pH around 7.
Thus, the salts with a pH value greater than 7 are:
**I. Sodium carbonate and IV. Sodium hydrogen carbonate.**
