The `pK_(a)` of an indicator is 4. Its pH range is

Options

A. `1-3`
B. `3-5`
C. `5-8`
D. `8-12`

Answer

To determine the pH range of an indicator with a given pK_a value, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the pK_a Value**:
The pK_a of an indicator is a measure of the acidity of the indicator. In this case, we have pK_a = 4.

2. **Identify the pH Range**:
The pH range for an indicator is typically around its pK_a value. Specifically, the pH range can be approximated as:
\[ \text{pH range} = \text{pK}_a \pm 1 \]
This means that the pH range will extend one unit below and one unit above the pK_a value.

3. **Calculate the pH Range**:
- Lower limit of pH range:
\[ \text{pK}_a - 1 = 4 - 1 = 3 \]
- Upper limit of pH range:
\[ \text{pK}_a + 1 = 4 + 1 = 5 \]
Therefore, the pH range of the indicator is from 3 to 5.

4. **Conclusion**:
The pH range of the indicator with a pK_a of 4 is **3 to 5**.