If we look at a Lewis structure of ethane, we can see that it looks like this
H H
I I
C = C
I I
H H
Now this is 1 molecule of ethene, but it has multiple bonds that total more than 2. So, this dispels options answers 2 and 4. When we look at bonds, we rarely look in terms of totals.
Now, it can’t be answer 1, because molecules don’t bond together. They can stick together and pack themselves in more densely, but they NEVER bond. At that point you’re creating a brand new molecule.
The answer, then, is 3, because looking at this Lewis structure, we can see 1 double bond between the two atoms of Carbon.
