Answer & Explanation:
Every 1.0 mole of an atom or molecule contains Avogadro's no. of molecules (6.022 x 10 ²³).
1.0 mole of X contains → 6.022 x 10 ²³ atoms.
n moles of X contains → ??? atoms.
∴ no. of atoms in n moles of X = (n moles)(6.022 x 10 ²³) / (1.0 mole).
1.0 mole of AB₂ contains → 6.022 x 10 ²³ molecules.
n moles of AB₂ contains → ??? molecules.
∴ no. of molecules in n moles of compound AB₂ = (n moles)(6.022 x 10 ²³) / (1.0 mole).
∴ no. of atoms of A in n moles of compound AB₂ = (n moles)(6.022 x 10 ²³) / (1.0 mole).
∴ no. of atoms of B in n moles of compound AB₂ = 2 [(n moles)(6.022 x 10 ²³) / (1.0 mole)].