Which of the following compounds does NOT contain a polyatomic ion?

• A. CaCO_3
• B. NaCl
• C. NaNO_3
• D. K_2SO_4

Answer: (B)

Verified step by step guidance

1. Step 1: Understand what a polyatomic ion is. A polyatomic ion is a charged species (ion) composed of two or more atoms covalently bonded, that acts as a single ion in chemical reactions. Examples include carbonate (CO_3^{2-}), nitrate (NO_3^{-}), and sulfate (SO_4^{2-}).
2. Step 2: Examine each compound to identify if it contains a polyatomic ion. For CaCO_3, recognize that CO_3^{2-} (carbonate) is a polyatomic ion.
3. Step 3: For NaNO_3, identify NO_3^{-} (nitrate) as a polyatomic ion present in the compound.
4. Step 4: For K_2SO_4, identify SO_4^{2-} (sulfate) as a polyatomic ion present in the compound.
5. Step 5: For NaCl, note that it consists of Na^{+} and Cl^{-} ions, both of which are monatomic ions (single atoms), so NaCl does NOT contain a polyatomic ion.