Question

Diamond is a covalently-bonded substance made of pure carbon. Each carbon atom has six total electrons so this means carbon shares ________ electron(s) with other carbon atoms.
A. one
B. two
C. four
D. six

Answer 1

When two carbon atoms are covalently bonded together, they try to achieve an octet structure so their electrons are 4 in number while each of them donates their remaining 2 so they end up sharing 4.

Answer 2

A stable atom would need 8 valence electrons, so since its sharing, lets subtract. 

8 - 6 = 2

It needs only 2 valence electrons. 

Answer: 2