Select the favourable conditions required for the formation of oxyhaemoglobin at the alveoli.

The formation of oxyhaemoglobin (HbO₂) in the alveoli is governed by the oxygen‑haemoglobin dissociation curve, which is influenced by several physiological factors.

1. Partial pressure of oxygen (pO₂)
When pO₂ is high, as it is in the alveolar air (approximately 100 mm Hg), the driving force for O₂ to bind to haemoglobin increases. According to Le Chatelier’s principle, the reaction
$Hb\; +\; O$₂ ⇌ HbO₂
shifts to the right, producing more oxyhaemoglobin.

2. Partial pressure of carbon dioxide (pCO₂)
A low pCO₂ in the alveoli (around 40 mm Hg) reduces the formation of carbamino‑haemoglobin and diminishes the Bohr effect, which otherwise would lower haemoglobin’s affinity for O₂. Thus, low pCO₂ favors O₂ binding.

3. Hydrogen ion concentration (H⁺) / pH
Less H⁺ corresponds to a higher pH (alkalosis). The Bohr effect states that higher pH increases haemoglobin’s affinity for O₂, shifting the equilibrium toward HbO₂. Therefore, a reduced H⁺ concentration promotes oxyhaemoglobin formation.

4. Temperature
A lower temperature (approximately 37 °C or slightly below in the well‑ventilated alveoli) stabilises the oxyhaemoglobin complex. Higher temperatures favor the release of O₂, so a cooler environment supports binding.

Combining these factors—high pO₂, low pCO₂, reduced H⁺ (higher pH), and lower temperature—creates the most favourable conditions for haemoglobin to load oxygen in the alveoli.