Identify the factors that directly favor the unloading of oxygen from hemoglobin in the blood near metabolically active tissues. an exchange of ions in the erythrocytes the presence of a pressure gradient for oxygen an increase in blood temperature near the tissues a decrease in blood pH near the tissues

Both the reduction in blood pH near the tissues and increase in blood temperature near the tissues are correct.

Explanation:

In the blood, carbon dioxide reacts with water to produce hydrogen ions or protons and bicarbonate. With the increase in the level of carbon dioxide within the body, more generation of protons takes place, which eventually results in a decrease in blood pH.  

The increase in the levels of carbon dioxide and at the same time, the reduction in pH results in the reduction of hemoglobin affinity towards oxygen. This makes oxygen to get dissociate from the molecule of hemoglobin, and due to losing affinity, oxygen gets unloaded from the hemoglobin.  

Similarly, an increase in temperature because of enhanced muscular activity also makes low affinity of hemoglobin towards oxygen and thus also results in the unloading of oxygen from the hemoglobin within the blood. Hence, both a decrease in pH and an increase in temperature near the tissues resulting in the unloading of oxygen from the hemoglobin.  

i think the answer is b.