Which of the following ions is an oxyanion?

• A. NO_3^-
• B. SO_4^{2-}
• C. NH_4^+
• D. CN^-

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the definition of an oxyanion. An oxyanion is a polyatomic ion that contains oxygen atoms bonded to another element (usually a nonmetal).
2. Step 2: Examine each ion given in the problem to see if it contains oxygen atoms bonded to another element:
3. - \(\mathrm{NO_3^-}\) contains nitrogen and oxygen atoms, so it is an oxyanion.
4. - \(\mathrm{SO_4^{2-}}\) contains sulfur and oxygen atoms, so it is also an oxyanion.
5. - \(\mathrm{NH_4^+}\) contains nitrogen and hydrogen atoms but no oxygen, so it is not an oxyanion.
6. - \(\mathrm{CN^-}\) contains carbon and nitrogen atoms but no oxygen, so it is not an oxyanion.