Molarity of pure `D_(2)O` will be

Options

A. `55.56`
B. 1
C. 50
D. 10

Answer

To find the molarity of pure D₂O (deuterium oxide), we will follow a series of steps based on the definition of molarity and the properties of D₂O.

### Step-by-Step Solution:

1. **Understanding Molarity**:
Molarity (M) is defined as the number of moles of solute per liter of solution. It can be expressed mathematically as:
\[ M = \frac{n}{V} \]
where \( n \) is the number of moles of solute and \( V \) is the volume of the solution in liters.

2. **Density of D₂O**:
The density of pure D₂O is approximately 1 g/mL. This means that 1 mL of D₂O has a mass of 1 gram.

3. **Molecular Mass of D₂O**:
The molecular mass of D₂O is approximately 20 g/mol. This is calculated based on the atomic masses of deuterium (D) and oxygen (O):
- Deuterium (D) has an atomic mass of about 2 g/mol, and there are 2 deuterium atoms in D₂O.
- Oxygen (O) has an atomic mass of about 16 g/mol.
Thus, the molecular mass of D₂O = (2 × 2) + 16 = 20 g/mol.

4. **Calculating Moles in 1 L of D₂O**:
Since the density is 1 g/mL, 1 L (which is 1000 mL) of D₂O has a mass of:
\[ \text{Mass of 1 L of D₂O} = 1000 \, \text{mL} \times 1 \, \text{g/mL} = 1000 \, \text{g} \]
To find the number of moles of D₂O in 1000 g, we use the formula:
\[ n = \frac{\text{mass}}{\text{molecular mass}} = \frac{1000 \, \text{g}}{20 \, \text{g/mol}} = 50 \, \text{mol} \]

5. **Calculating Molarity**:
Now, we can calculate the molarity using the number of moles and the volume in liters:
\[ M = \frac{n}{V} = \frac{50 \, \text{mol}}{1 \, \text{L}} = 50 \, \text{mol/L} \]

### Final Answer:
The molarity of pure D₂O is **50 mol/L**.