2.23     explain the use of carbon dioxide in carbonating drinks and in fire extinguishers, in terms of its solubility and density

Carbon dioxide is dissolved in drinks at pressures higher than atmospheric pressure to make them fizzy.  Gases become more soluble in water as the pressure increases.

Since carbon dioxide is denser than air (and does not support combustion), it will settle on fires at ground level and exclude the less dense oxygen, extinguishing the fire.