Which two ions are most abundant in ocean water?

• A. K^+ and NO_3^-
• B. Na^+ and Cl^-
• C. Ca^{2+} and SO_4^{2-}
• D. Mg^{2+} and HCO_3^-

Answer: (B)

Verified step by step guidance

1. Understand that ocean water contains a variety of dissolved ions, but some are much more abundant than others due to their sources and chemical stability.
2. Recall that the most abundant cation (positively charged ion) in seawater is sodium, represented as \(\mathrm{Na^{+}}\), because it comes from the weathering of rocks and is highly soluble.
3. Recall that the most abundant anion (negatively charged ion) in seawater is chloride, represented as \(\mathrm{Cl^{-}}\), which pairs with sodium to maintain electrical neutrality.
4. Recognize that other ions like \(\mathrm{K^{+}}\), \(\mathrm{Ca^{2+}}\), \(\mathrm{Mg^{2+}}\), \(\mathrm{NO_3^{-}}\), \(\mathrm{SO_4^{2-}}\), and \(\mathrm{HCO_3^{-}}\) are present but in much smaller concentrations compared to \(\mathrm{Na^{+}}\) and \(\mathrm{Cl^{-}}\).
5. Therefore, the two most abundant ions in ocean water are \(\mathrm{Na^{+}}\) and \(\mathrm{Cl^{-}}\).