When electrons are added to the outermost shell of a $C$ atom, it forms which of the following species?

• A. A carbanion ($C{-}^1$)
• B. A carbene ($C:$)
• C. A free radical ($C•$)
• D. A carbocation ($C{+}^1$)

Answer: (A)

Verified step by step guidance

1. Recall that a neutral carbon (C) atom has 4 valence electrons in its outermost shell, as it is in group 14 of the periodic table.
2. Understand that adding electrons to the outermost shell means increasing the number of valence electrons beyond the neutral state.
3. Recognize the common carbon species based on electron count: a carbocation (C⁺) has lost an electron, a free radical (C•) has an unpaired electron, a carbene (C:) has two nonbonded electrons, and a carbanion (C⁻) has gained an extra electron.
4. Since adding electrons means gaining negative charge, the species formed will have more electrons than the neutral carbon atom, which corresponds to a carbanion (C⁻).
5. Therefore, when electrons are added to the outermost shell of a carbon atom, the species formed is a carbanion, represented as \(C^{\!-}\).