Which of the following has the highest molarity ?
(i) 4 g of NaOH per `100 cm^3` of water
(ii) 4 g of HCI per `100 cm^3` of water
(iii) 4 g of `H_2SO_4` per `100 cm^3` water

Explanation

To determine which of the given solutions has the highest molarity, we will calculate the molarity for each solution step by step.

### Step 1: Understand the formula for molarity
Molarity (M) is defined as the number of moles of solute per liter of solution. The formula is:
\[ \text{Molarity (M)} = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} \]

### Step 2: Calculate the molarity of NaOH
1. **Given data**: 4 g of NaOH in 100 cm³ of water.
2. **Molar mass of NaOH**: 40 g/mol.
3. **Calculate number of moles**:
\[ \text{Number of moles of NaOH} = \frac{\text{Given mass}}{\text{Molar mass}} = \frac{4 \text{ g}}{40 \text{ g/mol}} = 0.1 \text{ moles} \]
4. **Convert volume to liters**:
\[ 100 \text{ cm}^3 = 0.1 \text{ L} \]
5. **Calculate molarity**:
\[ \text{Molarity of NaOH} = \frac{0.1 \text{ moles}}{0.1 \text{ L}} = 1 \text{ M} \]

### Step 3: Calculate the molarity of HCl
1. **Given data**: 4 g of HCl in 100 cm³ of water.
2. **Molar mass of HCl**: 36.5 g/mol.
3. **Calculate number of moles**:
\[ \text{Number of moles of HCl} = \frac{4 \text{ g}}{36.5 \text{ g/mol}} \approx 0.1096 \text{ moles} \]
4. **Convert volume to liters**:
\[ 100 \text{ cm}^3 = 0.1 \text{ L} \]
5. **Calculate molarity**:
\[ \text{Molarity of HCl} = \frac{0.1096 \text{ moles}}{0.1 \text{ L}} \approx 1.096 \text{ M} \]

### Step 4: Calculate the molarity of H₂SO₄
1. **Given data**: 4 g of H₂SO₄ in 100 cm³ of water.
2. **Molar mass of H₂SO₄**: 98 g/mol.
3. **Calculate number of moles**:
\[ \text{Number of moles of H₂SO₄} = \frac{4 \text{ g}}{98 \text{ g/mol}} \approx 0.0408 \text{ moles} \]
4. **Convert volume to liters**:
\[ 100 \text{ cm}^3 = 0.1 \text{ L} \]
5. **Calculate molarity**:
\[ \text{Molarity of H₂SO₄} = \frac{0.0408 \text{ moles}}{0.1 \text{ L}} = 0.408 \text{ M} \]

### Step 5: Compare the molarities
- Molarity of NaOH = 1 M
- Molarity of HCl ≈ 1.096 M
- Molarity of H₂SO₄ = 0.408 M

### Conclusion
The solution with the highest molarity is HCl, with a molarity of approximately 1.096 M.

### Final Answer
**The solution with the highest molarity is (ii) 4 g of HCl per 100 cm³ of water.**