Write the formula of Pyrosulphuric acid:
A) H2S2O7
B) H2SO5
C) H2S2O8
D) None of these

Pyrosulphuric acid, also known as oleum, is a powerful acid derived from sulfuric acid (H₂SO₄). It is a compound of sulfur, oxygen, and hydrogen, and its chemical formula is H₂S₂O₇.

### Explanation of the Options:

1. **A) \( \text{H}_2\text{S}_2\text{O}_7 \)**:
- This is the correct formula for pyrosulphuric acid (oleum). It consists of two sulfur atoms, seven oxygen atoms, and two hydrogen atoms.

2. **B) \( \text{H}_2\text{SO}_5 \)**:
- This formula represents a different compound and is not related to pyrosulphuric acid.

3. **C) \( \text{H}_2\text{S}_2\text{O}_8 \)**:
- This formula suggests a compound with two sulfur atoms and eight oxygen atoms, which is also not pyrosulphuric acid.

4. **D) None of these**:
- This option would be incorrect since option A is the correct answer.

### Conclusion:
The correct answer is **A) \( \text{H}_2\text{S}_2\text{O}_7 \)**, which represents pyrosulphuric acid.