What is the role of Sulfur (IV) oxide in the reaction described in part c of this question?

It looks like you've sent the same photo again. I've already answered parts a) through f) of the flow chart question in our previous conversation.

Regarding the questions visible at the top of the page:

b)
To write an equation for the reaction, I need to know which specific reaction this question refers to. Please provide the context or the full question for part b).

c)
To determine the role of Sulphur (IV) oxide ($\text{SO}_2$) in the reaction, I need to know which specific reaction this question refers to. Sulphur (IV) oxide can act as a reducing agent, an oxidizing agent, or an acid anhydride depending on the reaction. Please provide the context or the full question for part c).