Lowest Oxidation number of an atom in a compound A 2 B is - 2 . The number of an electron in its valence shell is

Step-by-step solution

A 2 B → 2 A + + B - 2 , B - 2 has complete octet in its dianionic form, thus in its atomic state it has 6 electrons in its valence shell. As it has negative charge, it has acquired two electrons to complete its octet. If the lowest oxidation state of an atom is - 2 , this typically implies that the atom can gain two electrons to reach a stable configuration. Therefore, the number of valence electrons in that atom would be six, because gaining two electrons would fill its outer shell.