a$)$ Fill in the blanks. $)=(8p$

During the experiment, the pressure reading at the bottom of the absorption column should be $$ than the pressure reading at the top.

Packing materials can be made of various of materials such as

$$ or $$

When removing $S{O}_2$ and nitrogen oxides from flue gases, it is more appropriate to use a $$ solution for absorption instead of pure water.

Absorption is called $$ absorption if it is based only on the dissolution of the gas in liquid, and $$ absorption in the case of a reaction between the gas and the liquid component.