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 :

the answer would be a