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

Options

A. `6.023 xx 10^(23)` molecules
B. `1.376 xx 10^(26)` molecules
C. `1.667 xx 10^(21)` molecules
D. `4.346 xx 10^(20)` molecules

Explanation

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

### Step 1: Determine the mass of water in one drop.
Given that 1 ml of water contains 20 drops, we can find the mass of one drop.

- Since 1 ml of water has a mass of 1 gram, we can calculate the mass of one drop as follows:
\[ \text{Mass of one drop} = \frac{1 \text{ gram}}{20 \text{ drops}} = 0.05 \text{ grams} \]

### Step 2: Calculate the number of moles in one drop.
To find the number of moles, we use the formula:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]
The molar mass of water (H₂O) is approximately 18 g/mol.

- Therefore, the number of moles in one drop of water is:
\[ \text{Number of moles} = \frac{0.05 \text{ grams}}{18 \text{ g/mol}} \approx 0.00278 \text{ moles} \]

### Step 3: Calculate the number of molecules in one drop.
To find the number of molecules, we use Avogadro's number, which is approximately \(6.022 \times 10^{23}\) molecules/mol.

- The number of molecules in one drop can be calculated as follows:
\[ \text{Number of molecules} = \text{Number of moles} \times \text{Avogadro's number} \]
\[ \text{Number of molecules} = 0.00278 \text{ moles} \times 6.022 \times 10^{23} \text{ molecules/mol} \approx 1.673 \times 10^{21} \text{ molecules} \]

### Final Answer:
The number of molecules in a drop of water is approximately \(1.673 \times 10^{21}\) molecules.

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