(i) The chemical equation for the reaction when carbon (IV) oxide gas is passed over heated charcoal is:

Here are the solutions to the questions:

(b) (i) The chemical equation for the reaction when carbon (IV) oxide gas is passed over heated charcoal is:

$$\text{CO}_2\text{(g)} + \text{C(s)} \xrightarrow{\text{heat}} 2\text{CO(g)}$$

(b) (ii) One use of carbon (II) oxide is:

• As a reducing agent in the extraction of metals from their ores (e.g., iron from iron oxide).
• As a fuel.

(c)
Observation:
In Set I, the bulb will light up.
In Set II, the bulb will not light up.

Explanation:
Graphite (in Set I) is a good conductor of electricity because it has a layered structure with delocalized electrons that are free to move and carry charge. Diamond (in Set II) is a non-conductor of electricity because all its valence electrons are used in strong covalent bonds within its rigid tetrahedral structure, leaving no free electrons to conduct electricity.