sodium is very reactive because of its 1 valence electron in the 3s orbital therefore, it will easily form an ion to get rid of that valence electron and become isoelectronic with neon which has a full stable octet: 1s2 2s2 2p6 (octet in 2s2 2p6)
Na: 1s2 2s2 2p6 3s1 but if it loses the 1 valence electron in 3s it becomes
Na^1+: 1s2 2s2 2p6 (stable octet in 2s2 2p6 just like Ne)
oxygen is very reactive it an oxidizer in that because of its high electronegativity, it will readily accept electrons in ionic bonds and pull electrons toward itself in covalent bonds with less electronegative elements. It will form an ion of O^2- to gain 2 electrons in its outer valence electron shell going from 1s2 2s2 2p4 to 1s2 2s2 2p6 thereby having 8 valence electrons.
chlorine is also very reactive just like oxygen and for the same reasons but it unlike oxygen, it needs 1 more electron to become like a noble gas so it goes from Cl: 1s2 2s2 2p6 3s2 3p5 to
Cl^1-: 1s2 2s2 2p6 3s2 3p6 and it will be isoelectronic with Ar having 8 electrons in its highest energy level, (outer shell n = 3)
This leaves carbon. Carbon will form covalent compounds with other carbon atoms and with other nonmetals such as hydrogen, oxygen, nitrogen, phosphorous. It will also form covalent lattice structures such as graphite, diamond, Buckminsterfullerene. For these reasons, it is least likely to form an ion since it makes so many covalent structures due to its ability to sp hydridize and form covalent bonds with its 4 valence electrons.
Sodium,it reats in air,water etc