Answer is: 60.
In one molecule of C₂₀H₄₂S₃O₂, there is 2 atoms of oxygen (subscript after oxygen indicates number of atoms of oxygen in chemical (molecular) formula).
So, in 30 molecules of C₂₀H₄₂S₃O₂, there is: 30·2 = 60 atoms of oxygen.
It has 4 valance electrons.
24 gFeF3 x (1 mol FeF3/grams FeF3)
x (6.02x10^23 molecules FeF3/ 1 mol FeF3)
Just Calculate Molar Mass of FeF3 and plug into equation
The rows are called Periods.
