The molarity of NaOH solution obtained by dissolving 4g of it in 250 mL solution is :

Options

A. 0.4 M
B. 0.8 M
C. 0.2 M
D. 0.1 M

Explanation

To find the molarity of the NaOH solution, we can follow these steps:

### Step 1: Determine the mass of the solute
We are given that the mass of NaOH (the solute) is 4 grams.

### Step 2: Find the molar mass of NaOH
The molar mass of NaOH can be calculated by adding the atomic masses of its constituent elements:
- Sodium (Na): approximately 23 g/mol
- Oxygen (O): approximately 16 g/mol
- Hydrogen (H): approximately 1 g/mol

So, the molar mass of NaOH = 23 + 16 + 1 = 40 g/mol.

### Step 3: Calculate the number of moles of NaOH
The number of moles of NaOH can be calculated using the formula:
\[ \text{Number of moles} = \frac{\text{mass of solute (g)}}{\text{molar mass (g/mol)}} \]
Substituting the values:
\[ \text{Number of moles} = \frac{4 \text{ g}}{40 \text{ g/mol}} = 0.1 \text{ mol} \]

### Step 4: Convert the volume of the solution from mL to L
The volume of the solution is given as 250 mL. To convert this to liters:
\[ \text{Volume in L} = \frac{250 \text{ mL}}{1000} = 0.25 \text{ L} \]

### Step 5: Calculate the molarity of the solution
Molarity (M) is defined as the number of moles of solute per liter of solution:
\[ \text{Molarity} = \frac{\text{Number of moles}}{\text{Volume of solution in L}} \]
Substituting the values:
\[ \text{Molarity} = \frac{0.1 \text{ mol}}{0.25 \text{ L}} = 0.4 \text{ mol/L} \]

### Conclusion
The molarity of the NaOH solution is 0.4 mol/L.

---