A.i) The process shown is the manufacture of hydrochloric acid.

Here are the solutions to the questions you've provided.

a.i) The process shown is the manufacture of hydrochloric acid.

a.ii) Substance A is hydrogen chloride gas.

a.iii) The equation for the process in the absorption tower is:

$$\text{HCl(g)} + \text{H}_2\text{O(l)} \rightarrow \text{HCl(aq)}$$

b.i) Another catalyst that can be used for the Contact Process (where Vanadium (V) oxide is used) is platinum.

b.ii) Two reasons why vanadium (V) oxide is commonly used as a catalyst are:

• It is cheaper than platinum.