A) Solutions P (pH 1, strong acid) and S (pH 14, strong base) would react together to give a solution with a pH of 7.0 through a neutralization reaction.

a) Solutions P (pH 1, strong acid) and S (pH 14, strong base) would react together to give a solution with a pH of 7.0 through a neutralization reaction.
Answer: P and S

i) The compound used to absorb carbon (IV) oxide gas from the air is calcium hydroxide or sodium hydroxide.
Answer: Calcium hydroxide (or Sodium hydroxide)

ii) Water vapour is removed from the air by cooling the air to a very low temperature, which causes the water vapour to condense into liquid water or freeze into ice. This prevents it from freezing and blocking pipes during the fractional distillation process.

iii) The gases in the air are liquefied by cooling them to very low temperatures, typically around $-200 \text{ °C}$ or below.