Answer:
The answer is there are 9.57 x 10²⁰ number of Cl atoms in 0.0728 g of PCl₃.
Number of moles = mass / molar mass
Mass of PCl₃ = 0.0728 g and molar mass of PCl₃ = 137.33g/mol
Number of moles of PCl₃ = 0.0728 / 137.33 = 5.3 x 10⁻⁴
In one mole there are Avogadro’s number of molecules that is 6.02 x 10²³
So, in 5.3 x 10⁻⁴ moles of PCl₃, there are =5.3 x 10⁻⁴ x 6.02 x 10²³ = 3.19 x 10²⁰
Now there is 3 atoms of Cl in PCl₃ so in 3.19 x 10²⁰ molecules of PCl₃, number of Cl atoms = 3.19 x 10²⁰ x 3 = 9.57 x 10²⁰ atoms
