The number of valence electrons in the O2- ion is.

The number of valence electrons in the oxide ion (O2-) is 8. A neutral oxygen atom has an atomic number of 8, with an electronic configuration of 1s² 2s² 2p⁴, meaning it possesses six valence electrons in its outermost shell. To achieve a stable noble gas configuration, oxygen gains two additional electrons to form the O2- anion. This addition results in a total of 10 electrons, with the electronic configuration becoming 1s² 2s² 2p⁶. In this state, the second shell (n=2) becomes the outermost shell and is completely filled with 8 electrons (2 in the 2s subshell and 6 in the 2p subshell). This configuration is isoelectronic with the noble gas neon, fulfilling the octet rule for maximum stability [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 46