**Core Concept**
The affinity of oxygen with hemoglobin is determined by various factors, including pH, temperature, and the presence of certain organic phosphates. The Bohr effect describes how changes in pH and CO2 levels affect the binding of oxygen to hemoglobin.

**Why the Correct Answer is Right**
2,3-Bisphosphoglycerate (2,3-BPG) is an organic phosphate that binds to hemoglobin, causing a conformational change that decreases its affinity for oxygen. This results in a right shift of the oxygen-hemoglobin dissociation curve, allowing for easier release of oxygen to tissues. The binding of 2,3-BPG to hemoglobin is crucial for adapting to changes in oxygen demand and facilitating gas exchange in the lungs and tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** Decreased H+ ions actually increase the affinity of oxygen with hemoglobin, as seen in the Bohr effect. An increase in pH (or decrease in H+ ions) shifts the oxygen-hemoglobin dissociation curve to the left, making it more difficult for oxygen to be released to tissues.

**Option C:** A decrease in temperature increases the affinity of oxygen with hemoglobin, as seen in the Bohr effect. Lower temperatures cause a left shift of the oxygen-hemoglobin dissociation curve, making it more difficult for oxygen to be released to tissues.

**Option D:** Decreased sorbitol is not directly related to the affinity of oxygen with hemoglobin. Sorbitol is an aldose that can accumulate in the blood due to diabetes mellitus, but it does not affect the binding of oxygen to hemoglobin.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the Bohr effect is a critical mechanism for regulating oxygen delivery to tissues. A decrease in pH (or increase in H+ ions) or an increase in CO2 levels can lead to a left shift of the oxygen-hemoglobin dissociation curve, making it more difficult for oxygen to be released to tissues. This is particularly relevant in conditions such as respiratory acidosis or lactic acidosis.

✓ Correct Answer: B. 2,3 BPG. 2,3-Bisphosphoglycerate decreases the affinity of oxygen with hemoglobin.