The highest number of atoms is present in

CONCEPT:

Number of Atoms and Moles

• The number of atoms in a given sample can be calculated using the concept of moles and Avogadro's number (6.022 × 10²³ atoms per mole).
• Moles of a substance can be calculated using the formula:

  Moles = Mass of the substance (in grams) / Molar mass (in g/mol)

• The total number of atoms is then given by:

  Number of Atoms = Moles × Avogadro's number

EXPLANATION

1) 0.40 g Ca:

• Molar mass of Ca = 40 g/mol
• Moles of Ca = 0.40 g / 40 g/mol = 0.01 mol
• Number of Atoms = 0.01 mol × 6.022 × 10²³ = 6.022 × 10²¹

2) 12 g He:

• Molar mass of He = 4 g/mol
• Moles of He = 12 g / 4 g/mol = 3 mol
• Number of Atoms = 3 mol × 6.022 × 10²³ = 1.8066 × 10²⁴

3) 4 g He:

• Molar mass of He = 4 g/mol
• Moles of He = 4 g / 4 g/mol = 1 mol
• Number of Atoms = 1 mol × 6.022 × 10²³ = 6.022 × 10²³

4) 46 g Na:

• Molar mass of Na = 23 g/mol
• Moles of Na = 46 g / 23 g/mol = 2 mol
• Number of Atoms = 2 mol × 6.022 × 10²³ = 1.2044 × 10²⁴

Comparing the number of atoms: The highest number of atoms is in 12 g He.

Therefore, the answer is 12 g He.