Atoms, elements and formulae

This task is about diagrams and chemical formulae for compounds.
These symbols represent atoms of different elements.
 
oxygen Oxygen (O) sulphur Sulphur (S)
hydrogen Hydrogen (H) sodium Sodium (Na)
carbon Carbon (C)    
 
a)
Write the formula for each of the following.
 
  i)
diagram 1
 
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  ii)
diagram 2
 
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  iii)
diagram 3
 
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b)
Using the symbols above, draw diagrams to represent each of the following.
 
  i)
H2O
 
  ii)
H2SO4
 
  iii) carbon dioxide