In how many of the following compounds of sulphur, there is S-S bond (only single bond not double bond between two sulphur atoms.)
`H_2S_2O_4, H_2S_2O_3, H_2S_2O_5, H_2S_2O_6, H_2S_2O_7, H_2S_2O_8, S_2Cl_2, "cyclic"(SO_3)_3`.

Explanation

To determine how many of the given compounds of sulfur contain an S-S single bond, we will analyze each compound one by one.

### Step-by-Step Solution:

1. **H₂S₂O₄ (Dithionic acid)**:
- Structure: The compound has two sulfur atoms connected by a single bond (S-S) and is surrounded by oxygen atoms.
- Conclusion: Contains S-S single bond.

2. **H₂S₂O₃ (Thiosulfuric acid)**:
- Structure: The compound has a double bond between the two sulfur atoms (S=S).
- Conclusion: Does not contain S-S single bond.

3. **H₂S₂O₅ (Disulfur pentoxide)**:
- Structure: The compound has two sulfur atoms connected by a single bond (S-S) and has additional oxygen atoms.
- Conclusion: Contains S-S single bond.

4. **H₂S₂O₆ (Disulfur hexoxide)**:
- Structure: Similar to H₂S₂O₅, it has two sulfur atoms connected by a single bond (S-S).
- Conclusion: Contains S-S single bond.

5. **H₂S₂O₇ (Disulfur heptoxide)**:
- Structure: The compound has an oxygen atom between the two sulfur atoms (S-O-S), thus no direct S-S bond.
- Conclusion: Does not contain S-S single bond.

6. **H₂S₂O₈ (Disulfur octoxide)**:
- Structure: Similar to H₂S₂O₇, it has oxygen atoms between the sulfur atoms (S-O-S), thus no direct S-S bond.
- Conclusion: Does not contain S-S single bond.

7. **S₂Cl₂ (Disulfur dichloride)**:
- Structure: The compound has two sulfur atoms connected by a single bond (S-S) and two chlorine atoms.
- Conclusion: Contains S-S single bond.

8. **Cyclic (SO₃)₃ (Cyclic trimer of sulfur trioxide)**:
- Structure: The cyclic structure does not have any direct S-S bonds; instead, it consists of sulfur and oxygen in a cyclic arrangement.
- Conclusion: Does not contain S-S single bond.

### Final Count:
From the analysis:
- Compounds with S-S single bonds: H₂S₂O₄, H₂S₂O₅, H₂S₂O₆, S₂Cl₂.
- Total: **4 compounds** contain S-S single bonds.

### Answer:
**4**

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