1 Multiple Choice 1 point A drop of water contains of molecules of \( \mathrm{H}_{2} \mathrm{O} \). millions trillions thousands billions

To determine how many molecules of \( \mathrm{H}_{2} \mathrm{O} \) are in a drop of water, we can use the following information: 1. A typical drop of water has a volume of about \( 0.05 \) mL (milliliters). 2. The density of water is approximately \( 1 \, \text{g/mL} \), so \( 0.05 \, \text{mL} \) of water has a mass of about \( 0.05 \, \text{g} \). 3. The molar mass of water \( \mathrm{H}_{2} \mathrm{O} \) is approximately \( 18 \, \text{g/mol} \). 4. Using Avogadro's number, which is approximately \( 6.022 \times 10^{23} \) molecules/mol, we can calculate the number of molecules in the drop. Now, let's calculate the number of molecules step by step: 1. Calculate the number of moles of water in the drop: \[ \text{moles of } \mathrm{H}_{2} \mathrm{O} = \frac{\text{mass}}{\text{molar mass}} = \frac{0.05 \, \text{g}}{18 \, \text{g/mol}} \] 2. Calculate the number of molecules: \[ \text{number of molecules} = \text{moles} \times \text{Avogadro's number} \] Let's perform these calculations. First, calculate the moles of water: \[ \text{moles of } \mathrm{H}_{2} \mathrm{O} = \frac{0.05}{18} \approx 0.00278 \, \text{mol} \] Now, calculate the number of molecules: \[ \text{number of molecules} = 0.00278 \, \text{mol} \times 6.022 \times 10^{23} \, \text{molecules/mol} \approx 1.67 \times 10^{21} \, \text{molecules} \] This value is in the range of billions (specifically, it is approximately 1.67 billion molecules). Thus, the correct answer is: **billions**.