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Q.
An element $M$ has an atomic mass of $19$ and atomic number $9$, its ions is represented by
ManipalManipal 2011Classification of Elements and Periodicity in Properties
Solution:
Configuration of an element ${ }_{9} M=1 s^{2},\, 2 s^{2},\, 2 p^{5}$.
Hence, its ion will be $M ^{-}$ because it can easily gain one electron to have octet.