Which of the following is wrong regarding Searle's apparatus method in finding Young's modulus of a given wire?
(a) Average elongation of wire will be determined with a particular load while increasing the load and decreasing the load.
(b) Reference wire will be just taut and experimental wire will undergo elongation.
( c) Air bubble in the spirit level will be disturbed from the central position due to relative displacement between the wires due to elongation.
(d) Average elongation of the wires is to be determined by increasing the load attached to both the wires.

Answer

To solve the question regarding Searle's apparatus method for finding Young's modulus of a given wire, we need to analyze each of the provided statements and determine which one is incorrect.

### Step-by-Step Solution:

1. **Understanding Searle's Apparatus Setup**:
- Searle's apparatus consists of two wires: a reference wire and an experimental wire. The reference wire remains taut while the experimental wire undergoes elongation when weights are applied.

2. **Analyzing Statement (a)**:
- **Statement**: Average elongation of wire will be determined with a particular load while increasing the load and decreasing the load.
- **Evaluation**: This statement is correct. The average elongation is calculated by noting the elongation when the load is increased and again when it is decreased.

3. **Analyzing Statement (b)**:
- **Statement**: Reference wire will be just taut and experimental wire will undergo elongation.
- **Evaluation**: This statement is also correct. The reference wire remains taut, while the experimental wire is the one that elongates under the applied load.

4. **Analyzing Statement (c)**:
- **Statement**: Air bubble in the spirit level will be disturbed from the central position due to relative displacement between the wires due to elongation.
- **Evaluation**: This statement is correct. The elongation of the experimental wire causes a relative displacement that affects the position of the air bubble in the spirit level.

5. **Analyzing Statement (d)**:
- **Statement**: Average elongation of the wires is to be determined by increasing the load attached to both the wires.
- **Evaluation**: This statement is incorrect. In Searle's apparatus, only the load attached to the experimental wire is increased; the reference wire does not have additional loads applied to it.

### Conclusion:
The incorrect statement regarding Searle's apparatus method in finding Young's modulus is **(d)**.