Question

to become stable, a carbon atom must share how many electrons?

Answer 1

Carbon has four valence electrons to start with. To be stable, it needs to have eight. So to get those eight, it needs how many more electrons?

Answer 2

To be balanced, an element must have eight valence electrons. Since Carbon have four valence electrons, it would have to be bonded to another element like Silicon that also has four valence electrons. Here's a link to a picture that will should how many valence electrons each element has.

http://images.tutorvista.com/cms/images/81/periodic-table-valence-electrons.png