Which of the following represents 1 g-molecule of the substance?

Options

A. `6*02xx10^(24)` molecules of `NH_(3)`
B. 4 g of helium
C. 40 g of CaO
D. 127 g of iodine.

Explanation

To determine which of the given options represents 1 g-molecule (or 1 mole) of a substance, we need to calculate the number of moles in each option using the formula:

\[ \text{Number of moles} = \frac{\text{Given weight (g)}}{\text{Molar mass (g/mol)}} \]

Let's analyze each option step by step.

### Step 1: Analyze the first option - 6.02 × 10²⁴ molecules of NH₃

1. **Identify the number of molecules**: 6.02 × 10²⁴ molecules.
2. **Use Avogadro's number**: 1 mole contains 6.02 × 10²³ molecules.
3. **Calculate the number of moles**:
\[ \text{Number of moles} = \frac{6.02 \times 10^{24} \text{ molecules}}{6.02 \times 10^{23} \text{ molecules/mole}} = 10 \text{ moles} \]
4. **Conclusion**: This option represents 10 moles, which is incorrect.

### Step 2: Analyze the second option - 4 grams of Helium (He)

1. **Given weight**: 4 grams.
2. **Molar mass of Helium**: 4 g/mol.
3. **Calculate the number of moles**:
\[ \text{Number of moles} = \frac{4 \text{ g}}{4 \text{ g/mol}} = 1 \text{ mole} \]
4. **Conclusion**: This option represents 1 mole, which is correct.

### Step 3: Analyze the third option - 40 grams of Carbon Monoxide (CO)

1. **Given weight**: 40 grams.
2. **Molar mass of CO**: Carbon (C) = 12 g/mol, Oxygen (O) = 16 g/mol, so CO = 12 + 16 = 28 g/mol.
3. **Calculate the number of moles**:
\[ \text{Number of moles} = \frac{40 \text{ g}}{28 \text{ g/mol}} \approx 1.43 \text{ moles} \]
4. **Conclusion**: This option does not represent 1 mole.

### Step 4: Analyze the fourth option - 127 grams of Iodine (I₂)

1. **Given weight**: 127 grams.
2. **Molar mass of I₂**: Iodine (I) = 127 g/mol, so I₂ = 2 × 127 = 254 g/mol.
3. **Calculate the number of moles**:
\[ \text{Number of moles} = \frac{127 \text{ g}}{254 \text{ g/mol}} = 0.5 \text{ moles} \]
4. **Conclusion**: This option does not represent 1 mole.

### Final Conclusion

The only option that represents 1 g-molecule (1 mole) of a substance is **4 grams of Helium**.

### Summary of Steps:
1. Calculate the number of moles for each substance using the formula.
2. Compare the calculated moles to 1 mole.
3. Identify the correct option.