Question

Lowest oxidation number of an atom in a compound $A_2B$ is -2. The number of electrons in its valence shell is:

Answer 1

A2B → 2A+ + B2−, B2− has a complete octet in its di-anionic form, thus in its atomic state it has 6 electrons in its valence shell. As it has a negative charge, it has acquired two electrons to complete its octet.