Answer:
4.2 × 10¹⁷ atoms of Se
Step-by-step explanation:
Step 1: Convert the mass to grams
We will use the conversion factor 1 g = 10⁶ μg.
55 μg × 1 g/10⁶ μg = 5.5 × 10⁻⁵ g
Step 2: Calculate the moles corresponding to 5.5 × 10⁻⁵ g of Se
The molar mass of Se is 78.96 g/mol.
5.5 × 10⁻⁵ g × 1 mol/78.96 g = 7.0 × 10⁻⁷ mol
Step 3: Calculate the atoms in 7.0 × 10⁻⁷ moles of Se
We will use Avogadro's number: there are 6.02 × 10²³ atoms of Se in 1 mole of Se.
7.0 × 10⁻⁷ mol × 6.02 × 10²³ atom/1 mol = 4.2 × 10¹⁷ atom