Comprehension # 2
The clouds consist of charged particles of water dispersed in air. Some of them are +vely charged, others are -vely charged. When +vely charged clouds come closer they cause lightening and thundering whereas when +ve and -ve charged colloids come closer they cause heavy rain by aggregation of minute particles. It is possible to cause artificial rain by throwing electrified sand or silver iodide from an aeroplane and thus coagulating the mist hanging in air.
Smoke screen is a cloud of smoke used to hide military, naval police etc. it consists of fine particles of `TiO_(2)`.
When excess of `AgNO_(3)` is treated with Kl solution, Agl forms

Options

A. `+ve " charged sol"`
B. `-ve " charged sol"`
C. neutral sol
D. True solution

Answer

To solve the problem regarding the formation of silver iodide (AgI) when excess AgNO3 is treated with KI solution, we can break it down into the following steps:

### Step 1: Understanding the Reaction
When potassium iodide (KI) is added to silver nitrate (AgNO3), a double displacement reaction occurs. The silver ions (Ag⁺) from AgNO3 react with the iodide ions (I⁻) from KI to form silver iodide (AgI), which is a precipitate.

**Hint:** Remember that in a double displacement reaction, the ions exchange partners to form new compounds.

### Step 2: Identifying the Excess Reactant
In this scenario, it is specified that there is an excess of AgNO3. This means that after the reaction, there will be unreacted Ag⁺ ions remaining in the solution because KI will react with only a portion of the Ag⁺ ions available.

**Hint:** Consider what happens when one reactant is in excess; it will influence the nature of the resulting solution.

### Step 3: Formation of Colloidal Solution
When AgI is formed, it can exist as a colloidal solution if the conditions are right. Colloidal solutions consist of fine particles that remain dispersed in a medium. The presence of excess AgNO3 means that the remaining Ag⁺ ions can lead to the formation of a positively charged colloidal solution of AgI.

**Hint:** Recall that colloidal solutions can be formed from precipitates under certain conditions, and the charge of the colloid depends on the ions present in excess.

### Step 4: Conclusion
Since there is an excess of AgNO3, the resulting AgI will form a positively charged colloidal solution due to the presence of unreacted Ag⁺ ions. Therefore, the correct conclusion is that AgI forms a positively charged sol.

**Hint:** Think about how the charge of the colloid is determined by the ions that remain in the solution after the reaction.

### Final Answer:
The correct option is that AgI forms a positively charged sol.