In lake test for `Al^(3+)` ions, there is the formation of coloured 'floating lake'. It is due to :

Options

A. Absorption of litmus by `[Al (OH)_(4)]^(-)`
B. Absorption of litmus by `Al(OH)_(3)`
C. Adsorption of litmus by `[Al(OH)_(4)]^(-)`
D. Adsorption of litmus by `Al(OH)_(3)`

Explanation

To solve the question regarding the formation of a colored 'floating lake' in the lead test for \( \text{Al}^{3+} \) ions, we can break it down into the following steps:

### Step 1: Understand the Lead Test for \( \text{Al}^{3+} \) Ions
The lead test for \( \text{Al}^{3+} \) ions involves the addition of a reagent that reacts with aluminum ions to form a precipitate. In this case, aluminum hydroxide, \( \text{Al(OH)}_3 \), is formed.

**Hint:** Recall that aluminum ions react with hydroxide ions to form aluminum hydroxide.

### Step 2: Identify the Precipitate
When \( \text{Al}^{3+} \) ions are present in a solution and a hydroxide source is added, aluminum hydroxide, which is a white precipitate, is formed. This precipitate has unique properties.

**Hint:** Think about the characteristics of aluminum hydroxide and its appearance in a solution.

### Step 3: Understand the Concept of Adsorption
Aluminum hydroxide has the ability to adsorb certain substances. In this case, it can adsorb blue litmus dye. When blue litmus is added to the solution, the aluminum hydroxide precipitate adsorbs the dye.

**Hint:** Consider how adsorption differs from absorption and how it can affect the color of a solution.

### Step 4: Formation of the Colored 'Floating Lake'
As aluminum hydroxide adsorbs the blue litmus dye, it changes color. The precipitate appears blue due to the adsorbed dye, creating a 'floating lake' effect on the surface of the colorless solution below.

**Hint:** Visualize how the colored precipitate would appear in contrast to the clear solution underneath.

### Step 5: Identify the Correct Explanation
The correct explanation for the formation of the colored 'floating lake' is due to the adsorption of blue litmus by aluminum hydroxide \( \text{Al(OH)}_3 \).

**Hint:** Look for the option that specifically mentions the interaction between aluminum hydroxide and blue litmus.

### Conclusion
The answer to the question is that the formation of the colored 'floating lake' is due to the adsorption of blue litmus by \( \text{Al(OH)}_3 \) (aluminum hydroxide).

**Final Answer:** The correct option is: "Adsorption of litmus by \( \text{Al(OH)}_3 \)".