The largest number of molecules in

Options

A. 36 g of water
B. 28 g of CO
C. 46 g of ethyl alcohol
D. 54 g of nitrogen pentaoxide `(N_(2)O_(5))`

Explanation

To solve the question of finding the largest number of molecules among the given substances, we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept**: The number of molecules in a substance can be calculated using the formula:
\[ \text{Number of molecules} = \text{Number of moles} \times N_A \]
where \(N_A\) is Avogadro's number (approximately \(6.022 \times 10^{23}\) molecules/mole). Therefore, the number of molecules is directly proportional to the number of moles.

2. **Calculate Moles for Each Substance**:
- **For H2O (Water)**:
- Given mass = 36 g
- Molar mass of H2O = 18 g/mol
- Calculate moles:
\[ \text{Moles of H2O} = \frac{\text{mass}}{\text{molar mass}} = \frac{36 \text{ g}}{18 \text{ g/mol}} = 2 \text{ moles} \]

- **For CO (Carbon Monoxide)**:
- Given mass = 28 g
- Molar mass of CO = 28 g/mol
- Calculate moles:
\[ \text{Moles of CO} = \frac{28 \text{ g}}{28 \text{ g/mol}} = 1 \text{ mole} \]

- **For C2H5OH (Ethyl Alcohol)**:
- Given mass = 46 g
- Molar mass of C2H5OH = 46 g/mol
- Calculate moles:
\[ \text{Moles of C2H5OH} = \frac{46 \text{ g}}{46 \text{ g/mol}} = 1 \text{ mole} \]

- **For N2O5 (Nitrogen Pentoxide)**:
- Given mass = 54 g
- Molar mass of N2O5 = 108 g/mol
- Calculate moles:
\[ \text{Moles of N2O5} = \frac{54 \text{ g}}{108 \text{ g/mol}} = 0.5 \text{ moles} \]

3. **Compare the Number of Moles**:
- H2O: 2 moles
- CO: 1 mole
- C2H5OH: 1 mole
- N2O5: 0.5 moles

4. **Determine the Largest Number of Molecules**:
- Since the number of molecules is directly proportional to the number of moles, H2O has the largest number of molecules (2 moles) compared to CO, C2H5OH, and N2O5.

5. **Conclusion**:
- The substance with the largest number of molecules is H2O (water).

### Final Answer:
The largest number of molecules is found in **H2O (Water)**.

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