Calculate the number of atoms in each of the following :
52u of He

Answer

To calculate the number of atoms in 52 u (atomic mass units) of helium (He), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the atomic mass of helium**:
The atomic mass of a helium atom is approximately 4 u (atomic mass units).

2. **Use Avogadro's number**:
Avogadro's number (N_A) is \(6.022 \times 10^{23}\) atoms/mol, which tells us how many atoms are in one mole of a substance.

3. **Determine the number of moles in 52 u of helium**:
To find the number of moles of helium in 52 u, we can use the formula:
\[ \text{Number of moles} = \frac{\text{mass in u}}{\text{atomic mass in u}} = \frac{52 \text{ u}}{4 \text{ u}} = 13 \text{ moles} \]

4. **Calculate the number of atoms**:
Now, we can calculate the total number of atoms using Avogadro's number:
\[ \text{Number of atoms} = \text{Number of moles} \times N_A = 13 \text{ moles} \times 6.022 \times 10^{23} \text{ atoms/mole} \]

5. **Perform the multiplication**:
\[ \text{Number of atoms} = 13 \times 6.022 \times 10^{23} \approx 7.8286 \times 10^{24} \text{ atoms} \]

6. **Express in scientific notation**:
The final result can be rounded to:
\[ \text{Number of atoms} \approx 7.83 \times 10^{24} \text{ atoms} \]

### Final Answer:
The number of atoms in 52 u of helium is approximately \(7.83 \times 10^{24}\) atoms.

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