If `1` ml of water contains `20` drops. Then no. of molecules in a drop of water is

Options

A. `6.023xx10^(23)`
B. `1.376xx10^(26)`
C. `1.673xx10^(21)`
D. `4.346xx10^(20)`

Explanation

To determine the number of molecules in a drop of water, we can follow these steps:

1. **Determine the mass of water in one drop**:
- Given: 1 ml of water contains 20 drops.
- Since the density of water is approximately \(1 \text{ g/ml}\), 1 ml of water has a mass of 1 gram.
- Therefore, the mass of one drop of water is:
\[ \text{Mass of one drop} = \frac{1 \text{ g}}{20 \text{ drops}} = 0.05 \text{ g} \]

2. **Calculate the number of molecules in 1 gram of water**:
- Given: 18 grams of water contains \(6.022 \times 10^{23}\) molecules (Avogadro's number).
- Therefore, the number of molecules in 1 gram of water is:
\[ \text{Number of molecules in 1 g} = \frac{6.022 \times 10^{23}}{18} \]
- Simplifying this:
\[ \text{Number of molecules in 1 g} = 3.345 \times 10^{22} \]

3. **Calculate the number of molecules in one drop of water**:
- Since 1 gram of water contains \(3.345 \times 10^{22}\) molecules and 1 gram of water is equivalent to 20 drops:
\[ \text{Number of molecules in one drop} = \frac{3.345 \times 10^{22}}{20} \]
- Simplifying this:
\[ \text{Number of molecules in one drop} = 1.6725 \times 10^{21} \]

Therefore, the number of molecules in a drop of water is approximately \(1.6725 \times 10^{21}\).