How many cl atoms are in 0.0728 g of pcl3?

The answer is there are 9.57 x 10²⁰ number of Cl atoms are 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