What statement is true?Group of answer choicesincreased CO2 causes pH to increaseincreased CO2 causes pH to decreasefreshwater has a higher pH than seawaterpH changed by the amount of dissolved oxygenin the deepr ocean pH is higher

Let's analyze each statement one by one:

1. Increased CO2 causes pH to increase:

   • When CO2 dissolves in water, it forms carbonic acid (H2CO3), which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). The increase in hydrogen ions causes the pH to decrease, not increase. Therefore, this statement is false.

2. Increased CO2 causes pH to decrease:

   • As explained above, the dissolution of CO2 in water leads to the formation of carbonic acid, which releases hydrogen ions, thereby lowering the pH. This statement is true.

3. Freshwater has a higher pH than seawater:

   • Generally, seawater has a slightly higher pH (around 8.1) compared to freshwater, which typically has a pH around 7. Therefore, this statement is false.

4. pH changed by the amount of dissolved oxygen:

   • While dissolved oxygen can influence pH, it is not the primary factor. The pH of water is more significantly affected by the presence of acids, bases, and CO2 levels. Therefore, this statement is misleading and generally false.

5. In the deep ocean pH is higher:

   • In the deep ocean, the pH is usually lower due to the accumulation of CO2 from the respiration of marine organisms and the decomposition of organic matter. Therefore, this statement is false.

Based on the analysis, the true statement is:

• Increased CO2 causes pH to decrease.