An acid indicator is represented by `Hl_(n).(K_(a)=10^(-5))`. The range of change of colour for the indicator is

Options

A. `3-5`
B. `4-6`
C. `5-7`
D. `6-8`

Explanation

To determine the range of change of color for the acid indicator represented by \( HIn \) with a dissociation constant \( K_a = 10^{-5} \), we can follow these steps:

### Step 1: Understand the Indicator
An acid-base indicator changes color based on the pH of the solution. The dissociation of the indicator can be represented as:
\[ HIn \rightleftharpoons H^+ + In^- \]

### Step 2: Determine the pKa
To find the pKa of the indicator, we can use the relationship:
\[ pK_a = -\log(K_a) \]
Given \( K_a = 10^{-5} \):
\[ pK_a = -\log(10^{-5}) = 5 \]

### Step 3: Determine the pH Range for Color Change
The color change of the indicator typically occurs around the pKa value. The general rule is that the color change occurs within one pH unit above and below the pKa. Therefore, the range of pH for the color change can be calculated as:
- Lower limit: \( pK_a - 1 = 5 - 1 = 4 \)
- Upper limit: \( pK_a + 1 = 5 + 1 = 6 \)

### Step 4: Conclusion
Thus, the range of change of color for the indicator \( HIn \) is between pH 4 and pH 6.

### Final Answer:
The range of change of color for the indicator is from pH 4 to pH 6.

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