Bohr effect is associated with effect of which of the following on oxygen affinity?

The decrease in O2 affinity of hemoglobin when the pH of blood falls is called the Bohr effect and is closely related to the fact that deoxygenated hemoglobin (deoxy-hemoglobin) binds H+ more actively than does oxygenated hemoglobin (oxy-hemoglobin). The pH of blood falls as its CO2 content increases, so that when the PCO2 rises, the curve shifts to the right and the P50 rises. Most of the unsaturation of hemoglobin that occurs in the tissues is secondary to the decline in the PO2, but an extra 1-2% unsaturation is due to the rise in PCO2 and consequent shift of the dissociation curve to the right. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 36.