Answer
(a)$Mg^{2+}$, it is monoatomic and it is a cation
(b) $SO_{3} ^{2-}$, it is polyatomic and it is an anion
(c) $Cu^{1+}$, it is monoatomic and it is a cation
(d) $NH_{4} ^{1+} $it is polyatomic and it is a cation
(e)$O^{2-}$ it is monoatomic and it is an anion
Work Step by Step
Most of these answers can be found in table 2.2. To decide if it is mono - or polyatomic you have to count the number of atoms which make up the molecule: if the number is more than one, it is polyatomic; otherwise it is monoatomic.
An anion is a molecule with a negative charge, and a cation is a molecule with a positive charge.
