Question

why does carbon tend to not gain or lose electrons?
because it has four valence electrons, so it would need to gain or lose four electrons to have a full valence shell
because it is a nonmetal
because it is in period 2
all of these

Explanation:

Carbon has four valence electrons. Gaining four electrons (to form \(C^{4 -}\)) would be difficult as the electron - electron repulsion would be high. Losing four electrons (to form \(C^{4+}\)) would require a large amount of energy to remove four electrons from the valence shell. The fact that it is a non - metal (but many non - metals like oxygen gain electrons) and being in period 2 (other period 2 elements like lithium lose electrons) are not the main reasons. The key is the number of valence electrons.

Answer:

Because it has four valence electrons, so it would need to gain or lose four electrons to have a full valence shell.