Lead nitrate solution is added to a test tube containing potassium iodide solution.

(a) Write the name and colour of the compound precipitated.

(b) Write the balanced chemical equation for the reaction involved.

(c) Name the type of this reaction justifying your answer.

OR

What happens when food materials containing fats and oils are left for a long time? List two observable changes and suggest three ways by which this phenomenon can be prevented.

(a) Name and colour of the compound precipitated:

• Name: Lead iodide
• Colour: Yellow

(b) Balanced chemical equation for the reaction:

$$\text{Pb(NO}_3)_2(\text{aq}) + 2\text{KI}(\text{aq}) \rightarrow \text{PbI}_2(\text{s}) + 2\text{KNO}_3(\text{aq})$$

(c) Type of reaction and justification:

• Type: Double displacement reaction (also classified as a precipitation reaction).
• Justification: It is a double displacement reaction because there is a mutual exchange of ions between the reactants (lead ions $\text{Pb}^{2+}$ and potassium ions $\text{K}^+$ exchange their anions $\text{NO}_3^-$ and $\text{I}^-$) to form new compounds. It is also a precipitation reaction because an insoluble solid (yellow precipitate of lead iodide) is formed during the reaction.

---

OR

When food materials containing fats and oils are left for a long time, they undergo oxidation and become rancid.

Two observable changes:

1. Change in smell: The food develops an unpleasant, foul odour.
2. Change in taste: The taste of the food becomes bad and unpleasant.

Three ways to prevent this phenomenon (rancidity):

1. Adding antioxidants: Adding substances that prevent oxidation (antioxidants) to foods containing fats and oils.
2. Airtight packaging: Storing food in airtight containers, which slows down the rate of oxidation by limiting exposure to oxygen.
3. Flushing with nitrogen gas: Packaging food items (like potato chips) in bags flushed with an inert gas like nitrogen to prevent contact with oxygen.