The model below shows a carbide ion.

8 light grey and 6 dark grey balls sit at the center with 2 concentric black rings around them. The inner ring has 2 medium grey balls on it, and the outer ring has 8 medium grey balls on it. At bottom, a dark grey ball = +1, a light grey ball = 0, a medium grey ball = negative 1.

What could be done to change this carbide ion to a neutral carbon atom?

remove 2 electrons
add 2 electrons
remove 4 electrons
add 4 electrons