Which one of the following compounds contains the nitrite ion?

• A. Na_2SO_3
• B. Na_2CO_3
• C. NaNO_2
• D. NaNO_3

Answer: (C)

Verified step by step guidance

1. Identify the nitrite ion by its chemical formula. The nitrite ion is represented as \(\mathrm{NO_2^-}\), which consists of one nitrogen atom and two oxygen atoms with an overall negative charge of one.
2. Examine each compound's formula to see if it contains the nitrite ion \(\mathrm{NO_2^-}\). For example, \(\mathrm{Na_2SO_3}\) contains the sulfite ion \(\mathrm{SO_3^{2-}}\), and \(\mathrm{Na_2CO_3}\) contains the carbonate ion \(\mathrm{CO_3^{2-}}\).
3. Look at \(\mathrm{NaNO_2}\), which contains sodium (\(\mathrm{Na^+}\)) and the \(\mathrm{NO_2^-}\) ion, matching the nitrite ion formula.
4. Check \(\mathrm{NaNO_3}\), which contains the nitrate ion \(\mathrm{NO_3^-}\), different from the nitrite ion because it has three oxygen atoms instead of two.
5. Conclude that the compound containing the nitrite ion \(\mathrm{NO_2^-}\) is \(\mathrm{NaNO_2}\).