If the volume of a drop of water is `0.0018 mL` then the number of water molecules present in two drop of water at room temperature is :

Options

A. `12.046xx10^(19)`
B. `1.084 xx10^(18)`
C. `4.48 xx 10^(17)`
D. `6.023 xx10^(23)`

Answer

To find the number of water molecules present in two drops of water, we can follow these steps:

### Step 1: Calculate the volume of two drops of water
Given that the volume of one drop of water is \(0.0018 \, \text{mL}\), the volume of two drops is:
\[ \text{Volume of two drops} = 2 \times 0.0018 \, \text{mL} = 0.0036 \, \text{mL} \]

### Step 2: Calculate the mass of water in two drops
The density of water is \(1 \, \text{g/mL}\). Therefore, the mass of water can be calculated using the formula:
\[ \text{Mass} = \text{Density} \times \text{Volume} \]
Substituting the values:
\[ \text{Mass} = 1 \, \text{g/mL} \times 0.0036 \, \text{mL} = 0.0036 \, \text{g} \]

### Step 3: Calculate the number of moles of water
To find the number of moles, we use the molar mass of water, which is \(18 \, \text{g/mol}\):
\[ \text{Number of moles} = \frac{\text{Mass}}{\text{Molar mass}} = \frac{0.0036 \, \text{g}}{18 \, \text{g/mol}} = 2 \times 10^{-4} \, \text{moles} \]

### Step 4: Calculate the number of water molecules
Using Avogadro's number, which is approximately \(6.022 \times 10^{23} \, \text{molecules/mol}\), we can find the number of molecules:
\[ \text{Number of molecules} = \text{Number of moles} \times \text{Avogadro's number} \]
Substituting the values:
\[ \text{Number of molecules} = 2 \times 10^{-4} \, \text{moles} \times 6.022 \times 10^{23} \, \text{molecules/mol} \]
Calculating this gives:
\[ \text{Number of molecules} \approx 1.2044 \times 10^{20} \, \text{molecules} \]

### Final Answer
The number of water molecules present in two drops of water is approximately \(1.2044 \times 10^{20}\) molecules.

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