Which two ions are most abundant in ocean water?

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

Answer: (B)

Verified step by step guidance

1. Understand that ocean water contains a variety of dissolved ions, but the most abundant ions are those that contribute the most to its salinity.
2. Recall that the major ions in seawater are primarily sodium (Na^+) and chloride (Cl^-), which together make up the majority of the dissolved salts.
3. Recognize that other ions like Ca^{2+}, SO_4^{2-}, Mg^{2+}, HCO_3^-, K^+, and NO_3^- are present but in much smaller concentrations compared to Na^+ and Cl^-.
4. Use knowledge of seawater composition, which shows that Na^+ and Cl^- ions dominate due to their high concentration and role in ocean salinity.
5. Conclude that the two most abundant ions in ocean water are Na^+ and Cl^-.