(a)

(i)  The bend is a condition that occurs in scuba divers. They have to breathe air under high pressure under water. Nitrogen gas does not dissolve in normal pressure. Under water, they will dissolve in the blood. Once the divers have risen, the gases escape the blood by forming N₂ bubbles in the blood. These bubbles can block capillaries and block O₂ flow, creating a painful bending condition.

(ii) At very high altitudes, atmospheric pressure is low and reduces the dissolution of oxygen in the blood and tissues of people traveling or living at very high altitudes. Lack of oxygen causes weakness and mental problems, a condition known as anoxia.

(b) When a soda water bottle is opened at room temperature and normal pressure conditions, the pressure inside the bottle decreases and the melting of CO₂ decreases, thus causing the gas bubbles to evaporate in the fizzy state.