Question

The number of sulphur atoms present in 0.2 mole of sodium thiosulphate

Answer 1

sodium thiosulfate (Na2S2O3) 
no of atom =atomicity*no of moles *na = 2*0.2*6.022*10^23 =2.41*10^23

Answer 2

The molecular formula of Sodium thiosulphate is given below:

                           Na₂S₂O₃ 

This means that in every 1 mole of sodium thiosulphate there are 2 moles of Sulphur atoms.

Therefore;

If 1 mole of  Na₂S₂O₃  = 2 moles of sulphur
Then 0.2 moles of Na₂S₂O₃  = 2 × 0.2/1
                                             = 0.4 moles of sulphur.

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Use Avogadro's constant and the 0.4 moles of sulphur to calculate the number of sulphur atoms.
(Avogadro's law states that 1 mole of any substance contains 6.022 × 10²³ atoms or molecules)

1 mole = 6.022 × 10²³ atoms
0.4 moles = 6.022 × 10²³  × 0.4/1
                =  2.41 × 10²³

The number of sulphur atoms in 0.2 moles of Sodium thiosulphate is 2.41 × 10²³ atoms.