To determine which is an example of a polyatomic ion, let's first understand what a polyatomic ion is. A polyatomic ion is a charged chemical species (ion) composed of two or more atoms covalently bonded or of a metal complex that acts as a single unit. Here’s a breakdown of the provided options:
1. [tex]\( H_2 \)[/tex]: This is a diatomic molecule consisting of two hydrogen atoms bonded together. It is not an ion, nor is it polyatomic.
2. [tex]\( CO_3^{2-} \)[/tex]: This is the carbonate ion. It consists of one carbon atom and three oxygen atoms, making it a polyatomic species. Additionally, it carries a charge of -2, making it an ion. Therefore, [tex]\( CO_3^{2-} \)[/tex] is a polyatomic ion.
3. [tex]\( Mg^+ \)[/tex]: This is a monatomic ion of magnesium with a +1 charge. It consists of only one atom, so it is not polyatomic.
4. [tex]\( Ne^+ \)[/tex]: This is a monatomic ion of neon with a +1 charge. It is also composed of only one atom and is therefore not polyatomic.
From the options provided, [tex]\( CO_3^{2-} \)[/tex] is the correct answer because it is a polyatomic ion. It contains multiple atoms (carbon and oxygen) and carries a charge.
So, the correct answer is:
[tex]\[ \boxed{2} \][/tex]
This indicates that the carbonate ion ([tex]\( CO_3^{2-} \)[/tex]) is an example of a polyatomic ion.
