How many of the following salts:
i. `NH_(4)C_(2)H_(3)O_(2)` ii. `PhCOONH_(4)` iii. `NaC_(2)H_(3)O_(2)`
iv. `NH_(4)CI` v. `MgS` vi. `Na_(2)SO_(4)`
vii. `KCI`
a. Hydrolyse more in water at `25^(@)C`.
b. Do not hydrolyse.

Explanation

To determine how many of the given salts hydrolyze more in water at 25°C and which do not hydrolyze, we need to analyze each salt based on the strength of the acid and base from which they are derived.

### Step-by-Step Solution:

1. **Identify the salts and their components:**
- i. `NH4C2H3O2` (Ammonium acetate)
- ii. `PhCOONH4` (Ammonium benzoate)
- iii. `NaC2H3O2` (Sodium acetate)
- iv. `NH4Cl` (Ammonium chloride)
- v. `MgS` (Magnesium sulfide)
- vi. `Na2SO4` (Sodium sulfate)
- vii. `KCl` (Potassium chloride)

2. **Determine the nature of each salt:**
- **i. `NH4C2H3O2`:** Formed from a weak base (NH4OH) and a weak acid (acetic acid). It will hydrolyze.
- **ii. `PhCOONH4`:** Formed from a weak base (NH4OH) and a weak acid (benzoic acid). It will hydrolyze.
- **iii. `NaC2H3O2`:** Formed from a strong base (NaOH) and a weak acid (acetic acid). It will hydrolyze.
- **iv. `NH4Cl`:** Formed from a strong acid (HCl) and a weak base (NH4OH). It will hydrolyze.
- **v. `MgS`:** Formed from a strong base (Mg(OH)2) and a weak acid (H2S). It will hydrolyze.
- **vi. `Na2SO4`:** Formed from a strong acid (H2SO4) and a strong base (NaOH). It will not hydrolyze.
- **vii. `KCl`:** Formed from a strong acid (HCl) and a strong base (KOH). It will not hydrolyze.

3. **Count the salts that hydrolyze:**
- The salts that hydrolyze more in water at 25°C are:
- `NH4C2H3O2`
- `PhCOONH4`
- `NaC2H3O2`
- `NH4Cl`
- `MgS`
- Total: 5 salts hydrolyze.

4. **Count the salts that do not hydrolyze:**
- The salts that do not hydrolyze are:
- `Na2SO4`
- `KCl`
- Total: 2 salts do not hydrolyze.

### Final Answer:
a. **5 salts hydrolyze more in water at 25°C.**
b. **2 salts do not hydrolyze.**