Answer : The correct answer is option A : They are anions.
Explanation :
Polyatomic ions are the ions that contain 2 or more different atoms that are covalently bonded to each other.
Polyatomic ions could be positively charged ( Cations) or negatively charged (anions).
But if we take a look at the most commonly known polyatomic ions, we will see that almost all of them are anions .
Some examples are given below.
Nitrate : NO₃⁻
Sulfate : SO₄²⁻
Hydroxide : OH⁻
Phosphate : PO₄³⁻
Chlorate : ClO₃⁻
The only positively charged polyatomic ion that is most common is NH₄⁺ ion.
Hence we can say that, the characteristic that is shared by most simple polyatomic ions is that they are anions.