The number of atoms present in one mole of an element is equal to Avogadro number. Which of the following element contains the greatest number of atom?

Options

A. 4g He
B. 46g Na
C. 0.40g Ca
D. 12 g He

Explanation

To solve the question of which element contains the greatest number of atoms from the given options, we will follow these steps:

### Step 1: Understand the Concept of Moles
The number of atoms in one mole of any substance is equal to Avogadro's number, which is approximately \(6.022 \times 10^{23}\). Therefore, the number of atoms in a given mass of an element can be calculated by first determining the number of moles in that mass.

### Step 2: Use the Formula for Moles
The formula to calculate the number of moles (N) is:
\[ N = \frac{W}{M} \]
where:
- \(W\) = given weight of the element
- \(M\) = molar mass (molecular weight) of the element

### Step 3: Calculate Moles for Each Option
Now, we will calculate the number of moles for each of the given options:

1. **4 grams of Helium (He)**
- Molar mass of Helium = 4 g/mol
- Calculation:
\[ N = \frac{4 \text{ g}}{4 \text{ g/mol}} = 1 \text{ mole} \]

2. **46 grams of Sodium (Na)**
- Molar mass of Sodium = 23 g/mol
- Calculation:
\[ N = \frac{46 \text{ g}}{23 \text{ g/mol}} = 2 \text{ moles} \]

3. **0.4 grams of Calcium (Ca)**
- Molar mass of Calcium = 40 g/mol
- Calculation:
\[ N = \frac{0.4 \text{ g}}{40 \text{ g/mol}} = 0.01 \text{ moles} \]

4. **12 grams of Helium (He)**
- Molar mass of Helium = 4 g/mol
- Calculation:
\[ N = \frac{12 \text{ g}}{4 \text{ g/mol}} = 3 \text{ moles} \]

### Step 4: Compare the Number of Moles
Now we have the number of moles for each option:
- 4 grams of Helium: 1 mole
- 46 grams of Sodium: 2 moles
- 0.4 grams of Calcium: 0.01 moles
- 12 grams of Helium: 3 moles

### Step 5: Determine the Greatest Number of Atoms
Since the number of atoms is directly proportional to the number of moles, we can conclude:
- 12 grams of Helium has the greatest number of moles (3 moles), which means it has the greatest number of atoms.

### Final Answer
The element that contains the greatest number of atoms is **12 grams of Helium**.

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