CBSE Class 10 Science 2018 · Paper 31/1/C · Question 3

Carbon forms covalent compounds. Reason: to reach the stable electron arrangement of a noble gas by forming an ion, carbon would have to gain $4$ electrons, becoming ${\text{C}}^{4-}$ with an octet like neon, or lose $4$, becoming ${\text{C}}^{4+}$ with a duplet like helium. Gaining four is difficult, because a nucleus of $6$ protons cannot hold on to $10$ electrons, and losing four needs a very large amount of energy. So carbon shares its $4$ valence electrons with other atoms (of carbon or of other elements), forming covalent bonds. Example: methane, ${\text{CH}}_4$ (any other covalent compound of carbon, such as ethane or carbon dioxide, is also correct).