**Core Concept**
The affinity of oxygen for hemoglobin (Hb) is influenced by various physiological and biochemical factors. The Bohr effect describes a decrease in oxygen affinity for Hb in response to an increase in carbon dioxide (CO2) levels or a decrease in pH (acidosis), facilitating the release of oxygen to tissues.

**Why the Correct Answer is Right**
The Bohr effect is a result of the binding of hydrogen ions (H+) to the hemoglobin molecule, which causes a conformational change that reduces the affinity of oxygen for Hb. This is mediated by the alpha-globin chains, which undergo a histidine residue (His 146) that binds to H+. The binding of H+ to His 146 reduces the binding of oxygen to the heme group, allowing for increased oxygen release to tissues. This mechanism is essential for maintaining adequate tissue oxygenation, especially during conditions of increased metabolic activity or acidosis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option does not accurately describe the relationship between oxygen affinity and pH. While a decrease in pH does affect oxygen affinity, this option does not specify the Bohr effect.
* **Option B:** This option is incorrect because the Haldane effect refers to the increased binding of oxygen to Hb in response to increased CO2 levels, not a decrease in affinity.
* **Option C:** This option is incorrect as it refers to the Root effect, which is a different mechanism that affects the affinity of hemoglobin for oxygen in certain fish species, not humans.

**Clinical Pearl / High-Yield Fact**
The Bohr effect is an essential mechanism that allows for the regulation of oxygen delivery to tissues. Understanding this concept is crucial for interpreting acid-base disturbances and their impact on oxygen delivery in critically ill patients.

**Correct Answer:** B. The Bohr effect.