To draw a Lewis structure, first add the number of outer (valence) electrons contributed by each atom to obtain the total number of outer electrons. What is this value for a molecule of H2CCH2?

12 is the total number of outer electrons  for a molecule of

Explanation:

Lewis-dot structure : It shows the bonding between the atoms of a molecule and it also shows the unpaired electrons present in the molecule.

In the Lewis-dot structure the valance electrons are shown by 'dot'.

Valence electron of carbon = 4

Valence electron of hydrogen = 1

Number of carbon atoms in = 2

Number of hydrogen atoms in = 4

Total number of valence electrons :

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c is having 4 valence electrons and is bonded to three hydrogens and one sulphur atom, therefore, the number of bond pair is equal to four. as all the valence electrons are used in forming the bonds so, there is no lone pair left on carbon.

s is having 6 valence electrons and is bonded to one other sulfur atom and one carbon atom, therefore, the number of bond pair is equal to 2. as only two valence electrons are used in forming the bonds so, four electrons are left. therefore, two lone pairs are present on s.